Electrochemical devices comprising compressed gas solvent electrolytes

ABSTRACT

Disclosed are novel electrolytes, and techniques for making and devices using such electrolytes, which are based on compressed gas solvents. Unlike conventional electrolytes, disclosed electrolytes are based on “compressed gas solvents” mixed with various salts, referred to as “compressed gas electrolytes.” Various embodiments of a compressed gas solvent includes a material that is in a gas phase and has a vapor pressure above an atmospheric pressure at a room temperature. The disclosed compressed gas electrolytes can have wide electrochemical potential windows, high conductivity, low temperature capability and/or high pressure solvent properties.

PRIORITY CLAIM AND RELATED PATENT APPLICATION

This patent document claims priorities to and the benefits of (1) U.S.Provisional Application No. 61/905,057 entitled “ELECTROCHEMICAL ENERGYSTORAGE DEVICES BASED ON COMPRESSED GAS ELECTROLYTES,” and filed Nov.15, 2013, and (2) U.S. Provisional Application No. 61/972,101 entitled“ELECTROCHEMICAL ENERGY STORAGE DEVICES BASED ON COMPRESSED GASELECTROLYTES,” and filed Mar. 28, 2014, the entire contents of which areincorporated by reference in this document.

TECHNICAL FIELD

This patent document relates to conductive electrolytes, such asionically conductive electrolytes, which may be used in electrochemicalenergy storage devices, electroplating, or electrochemical sensing, anddevices and systems that use such electrolytes.

BACKGROUND

The energy density of batteries is proportional to the operatingvoltage. In supercapacitors (i.e., electrochemical double-layercapacitors) the energy density is proportional to voltage squared. Witha greater demand for increased energy densities in electrochemicalenergy storage devices, significant improvements can be made byincreasing the voltage ratings of such devices. An importantcontributing factor to the voltage limitation of electrochemical energystorage devices is the stability of the electrolyte solvent. Atincreased voltages, the electrolyte solvent may break down and increasein resistance. As a result, loss of charge storage capability(capacity), gassing and device end of life may be reached. Therefore,improving the voltage rating of such devices is highly dependent on theelectrolyte system used. Increasing the oxidation resistance of solventsmay widen the potential window of the electrolyte, defined as thepotential difference between which significant oxidation and reductioncurrent occurs, and can be very useful in electrochemical applicationssuch as batteries, supercapacitors, chemical sensing and commonreduction-oxidation electrochemistry.

SUMMARY

Disclosed are novel electrolytes, and techniques for making and devicesusing such electrolytes, which are based on compressed gas solvents.Unlike conventional electrolytes, disclosed electrolytes are based on“compressed gas solvents” mixed with various salts, referred to as“compressed gas electrolytes.” Various embodiments of a compressed gassolvent includes a material that is in a gas phase and has a vaporpressure above an atmospheric pressure at a room temperature.Electrochemical devices such as rechargeable batteries andsupercapacitors which use such compressed gas electrolytes are alsodisclosed. Also disclosed are techniques for electroplatingdifficult-to-deposit metals or alloys using compressed gas electrolytesas an electroplating bath. The disclosed compressed gas electrolytes canhave wide electrochemical potential windows, high conductivity, low orhigh temperature operation capability, high oxidation resistance, andbeneficial high pressure solvent or solid electrolyte interfaces (SEI)forming properties.

Conventional electrolytes use solvents that are in liquid phase undernormal atmospheric conditions, which defined as a pressure of 100 kPa,or one atmosphere, and a temperature of 293.15 K, or room temperature.In contrast, disclosed compressed gas electrolytes use a “compressed gassolvent” which has a vapor pressure above atmospheric pressure of 100kPa at room temperature of 293.15 K. Hence, without a proper pressurizedenvironment, such a compressed gas solvent is often in gas phase, whichis not suitable for forming electrolytes.

The disclosed techniques of making compressed gas electrolytes includeplacing a compressed gas solvent at a given temperature under acompressive pressure equal to, or greater than the compressed gassolvent's vapor pressure at that temperature. In some embodiments,compressed gas electrolytes is placed inside a rigid container tomaintain a sufficiently high pressure to keep the compressed gas solventin the liquid phase. The pressure required to maintain the liquid phasecan be applied either by the compressed gas solvent's own vapor pressureinside the rigid container, by an externally applied pressure inside therigid container, or by both of the above. Furthermore, compressed gaselectrolytes can use a single chemical solvent or a solvent composed ofmultiple different chemicals, wherein at least one of the composingchemicals is a compressed gas solvent. Moreover, one or more types ofcompressed gas solvents can be mixed with any number of solid or liquidchemicals to form a compressed gas solvent mixture. As commonly known,mixtures of various chemicals may greatly change the boiling, freezingor critical points associated with individual component of the mixture.Furthermore, the compressed gas solvent can also be made of mixturesthat are liquid under atmospheric conditions if at least one of thecomponents in the mixture is a compressed gas solvent. In someembodiments, to form the disclosed compressed gas electrolyte, any ofthe above-described compressed gas solvents or compressed gas solventmixtures is mixed with one or more types of salts. The compressed gaselectrolyte can then be used in various of devices as described below.

Electrochemical energy storage devices such as rechargeable batteriesand supercapacitors which use compressed gas electrolytes are alsodisclosed. A disclosed electrochemical energy storage device can includea pair of conducting electrodes and an ionically conducting electrolyteseparating the pair of conducting electrodes. The electrolyte furthercomprises a compressed gas solvent mixed with one or more types ofsalts, forming a “compressed gas electrolyte.” The compressed gassolvent used in the disclosed electrochemical energy storage device hasthe various properties as described above. For example, the compressedgas solvent has a vapor pressure above atmospheric pressure of 100 kPaat room temperature of 293.15 K. Moreover, the pair of conductingelectrodes and the compressed gas electrolyte are contained inside arigid housing which maintains a sufficiently high pressure to keep thecompressed gas solvent in the liquid phase. For example, the requiredhigh pressure is achieved either by the compressed gas solvent's ownvapor pressure inside the rigid housing or by an externally appliedpressure inside the rigid container, or by both of the above.

In some embodiments, the disclosed electrochemical energy storage deviceis a supercapacitor which includes an electrochemical electrode assemblythat comprises: a negative current collector; negative electrodematerial coated on the negative current collector;

a positive current collector; positive electrode material coated on thepositive current collector; and an electrically insulating separator.This electrochemical electrode assembly is placed inside the rigidhousing together with the compressed gas electrolyte to form anelectrochemical cell.

In some embodiments, one or both of the negative electrode material andthe positive electrode material include nanostructured material to formhigh surface area electrode, which includes one or more of: nanofibers;nanopillars; nanoparticle aggregates; nanoporous structures; and acombination of the above.

In some embodiments, to construct an electrochemical energy storagedevice based on the disclosed compressed gas electrolytes, a compressedgas electrolyte is first formed by mixing a compressed gas solvent andone or more types of salts into a high pressure container. Next, thecompressed gas electrolyte is inserted into the electrochemicalelectrode assembly inside the rigid housing to form an operatingelectrochemical cell. Alternatively, to construct an electrochemicalenergy storage device based on the disclosed compressed gaselectrolytes, a salt is first inserted into the electrochemicalelectrode assembly inside the rigid housing to form a salt loadedelectrochemical electrode assembly. Next, a compressed gas solvent isintroduced into the salt loaded electrochemical electrode assembly to bemixed with the salt to create the compressed gas electrolyte inside therigid housing, thereby form an operating electrochemical cell.

Also disclosed are techniques for electroplating difficult-to-depositmetals or alloys using compressed gas electrolytes as an electroplatingbath. In some embodiments, to electroplate a difficult-to-depositmaterial on an object, a compressed gas electrolyte is first prepared bymixing a compressed gas solvent and one or more types of salts, thecompressed gas solvent used has the various properties as describedabove. Next, using the compressed gas electrolyte as anelectrodepositing bath, an anode made of at least thehard-to-electroplate material is immersed in the compressed gaselectrolyte. A cathode made of an object that requires electroplating ofthe hard-to-electroplate material is also immersed in the compressed gaselectrolyte. Next, a proper voltage is applied to the anode and thecathode to allow transferring of the difficult-to-deposit material fromthe anode to the cathode through the compressed gas electrolyte.Moreover, the compressed gas electrolyte, the anode and the cathode areplaced inside a pressure chamber for providing a required pressure tokeep the compressed gas solvent in the liquid phase.

In one aspect, a disclosed electrochemical device includes an ionicallyconducting electrolyte that comprises a compressed gas solvent and oneor more types of salts. The compressed gas solvent includes a materialthat is in a gas phase and has a vapor pressure above an atmosphericpressure at a room temperature. The disclosed electrochemical devicealso includes a housing enclosing the ionically conducting electrolyteand structured to provide a pressurized condition to the compressed gassolvent. The disclosed electrochemical device additionally includes apair of conducting electrodes in contact with the ionically conductingelectrolyte.

The disclosed compressed gas electrolytes can have wide electrochemicalpotential windows, high conductivity, low temperature capability, andhigh pressure solvent properties. Examples of a class of chemicals thatcan be used as solvents for electrolytes include hydrofluorocarbons, inparticular fluoromethane, difluoromethane, tetrafluoroethane,pentafluoroethane, among others. Other classes of chemicals may be usedas solvents for electrolytes as well, e.g., hydrofluoroolefins,hydrofluorochlorocarbons, chlorofluorocarbons, among others. In someembodiments, compressed gas solvents having a composition which givesrise to high electronegativity (e.g., fluorine, chlorine, oxygen,nitrogen, etc.), high polarity, and oxidation resistance are desirable.Generally, any chemical having the above-described properties of acompressed gas solvent and having sufficiently high relativepermittivity and suitable solubility for salts to create a conductiveelectrolyte solution may be used. Applications of the disclosedcompressed gas electrolytes include electrochemical energy storage,electroplating and electrochemical sensing, among others.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates schematics of (A) an exemplary lithium-ion batteryand (B) an exemplary electrochemical double-layer capacitor(supercapacitor) including two charged electrodes separated by theelectrolyte.

FIG. 2 shows a schematic of a common supercapacitor device andequivalent resistances coupled in serials, each corresponding to arespective component of the supercapacitor device.

FIG. 3 presents a table listing detailed properties of commonlyavailable solvents compared with a proposed compressed gas solvent,difluoromethane, which is a fluorinated compressed gas solvent inaccordance with some embodiments.

FIG. 4 presents a table listing detailed properties of some of theproposed compressed gas solvents which may be good candidates forwider-potential-window electrochemical energy storage devices, andplating and sensing application, in accordance with some embodiments.

FIG. 5 shows a plot comparing vapor pressures of various proposedcompressed gas solvents over a wide temperature range in accordance withsome embodiments.

FIG. 6 illustrates an example of salt ions (with more negatively chargedions than positively charged ions) solvated in solvent molecules to formnegative charge carriers including both a solvated single ion andsolvated ion aggregates.

FIG. 7 illustrates an example of salt ions (with more positively chargedions than negatively charged ions) solvated in solvent molecules to formpositive charge carriers including both a solvated single ion andsolvated ion aggregates.

FIG. 8 shows conductivities vs. temperature plots of various electrolytesystems containing various solvents and the same salt, e.g., 0.02M ofTBAPF6 salt, in accordance with some embodiments.

FIG. 9 shows conductivities vs. temperature plots of compressed gassolvent difluoromethane with 0.02 M of various salts forming conductivecompressed gas electrolyte systems in accordance with some embodiments.

FIG. 10 shows conductivities vs. temperature plots of compressed gassolvent difluoromethane with different concentrations oftetrabutylammonium hexafluorophosphate (TBAPF6) salt in accordance withsome embodiments.

FIG. 11 shows conductivities vs. temperature plots of electrolytesystems containing fluoromethane and fluoroethane compressed gassolvents and lithium bis-trifluoromethanesulfonimide (LiTFSI) salt inaccordance with some embodiments.

FIG. 12 presents a table listing stability, dipole moment and GWP ofvarious proposed compressed gas solvents including fluorine-containingsolvents in accordance with some embodiments.

FIG. 13 shows cyclic voltammetry curves of electrolyte systems based onboth dichloromethane and difluoromethane solvents containing 0.02 MTEABF4 salt under a scan rate of 50 mV/s at room temperature inaccordance with some embodiments.

FIG. 14 shows cyclic voltammetry curves of difluoromethane containing0.02 M of different salts with a scan rate of 50 mV/s at roomtemperature in accordance with some embodiments.

FIG. 15 shows cyclic voltammetry curves for different solvent systemsusing LiTFSI or LiPF6 based salt with a scan rate of 100 mV/s at roomtemperature in accordance with some embodiments.

FIG. 16 shows measurements of pressure inside pressure vessel containingvolume of solvent for both isochoric increase in pressure in a volumeconstrained system and a purely vapor pressure based volumeunconstrained system in accordance with some embodiments.

FIG. 17 shows conductivity and pressure vs. temperature measurement ofdifluoromethane solvent containing 0.1 M TBAPF₆ salt under isochoricincrease in pressure of the solvent system in accordance with someembodiments.

FIG. 18 illustrates an ionically conducting electrolyte composed of amixture of salt and solvent inside an pressurized housing to form anelectrochemical cell in accordance with some embodiments.

FIG. 19 illustrates an electrochemical electrode assembly being packagedinside a device package to form an electrochemical cell in accordancewith some embodiments.

FIG. 20 presents a flowchart illustrating a process of filling theelectrochemical electrode assembly and housing, such as the onedescribed in FIG. 19 with a compressed gas electrolyte in accordancewith some embodiments.

FIG. 21 presents a flowchart illustrating another process of filling theelectrochemical electrode assembly and housing, such as the onedescribed in FIG. 19 with a compressed gas electrolyte solution inaccordance with some embodiments.

FIG. 22 shows cyclic voltammetry curves of two electrochemical doublelayer capacitors with equal mass electrodes using different solventscontaining 0.5 M TBAPF6 salt measured at room temperature with a scanrate of 10 mV/s in accordance with some embodiments.

FIG. 23 shows a zoomed in view of the cyclic voltammetry curves in FIG.22 in accordance with some embodiments.

FIG. 24 shows the resistance vs. cycle number curve of the double layercapacitor device containing difluoromethane and 0.5 M TBABF4 salt inaccordance with some embodiments.

FIG. 25 shows the leakage current vs. cycle number curve of the samedevice containing difluoromethane and 0.5 M TBABF4 salt in accordancewith some embodiments.

FIG. 26 shows the capacitance vs. cycle number curve of the same devicecontaining difluoromethane and 0.5 M TBABF4 salt in accordance with someembodiments.

FIG. 27 shows the impedance spectra of the same device at lowtemperatures in accordance with some embodiments.

FIG. 28 shows the resistance vs. temperature curve of the same device inaccordance with some embodiments.

FIG. 29 shows increase in resistance (%) vs. temperature curves ofdouble layer capacitor devices using difluoromethane and acetonitrilebased electrolytes in accordance with some embodiments.

FIG. 30 shows a cyclic voltammetry curve of the battery device usingfluoromethane compressed gas solvent containing 0.1 M LiTFSI saltmeasured with a sweep rate of 0.03 mV/s at room temperature inaccordance with some embodiments.

FIG. 31 shows an impedance spectra of the same device as in FIG. 30 inaccordance with some embodiments.

FIG. 32 illustrates packaging multiple electrochemical cells into asingle device assembly in accordance with some embodiments.

FIG. 33 illustrates an electrical controller composed of multipleenvironmental sensors and devises in accordance with some embodiments.

FIG. 34 shows using an environmental controller to monitor multipleelectrochemical device assemblies in accordance with some embodiments.

FIG. 35 shows multiple electrochemical device assemblies can be used topower an electrical load under the control of an electrical controllerin accordance with some embodiments.

FIG. 36 illustrates how charged carriers or ions in the high pressureelectrolyte can gain access to smaller nanopores of a high surface areacharged electrode surface by means of a higher pressure system inaccordance with some embodiments.

FIG. 37 shows example reactions and reaction products from differentcompressed gas solvents and lithium metal chemical reactions. Theseproducts are only some of the possible products from the possiblechemical reactions in accordance with some embodiments.

FIG. 38 shows the SEM images and XPS data of surface of lithium metalafter submerged into fluoromethane for five days at room temperature inaccordance with some embodiments.

FIG. 39 shows SEM images of the surface of lithium metal after submergedinto difluoromethane for five days at room temperature in accordancewith some embodiments.

FIG. 40 shows SEM images of the surface of lithium metal after submergedinto tetrafluoroethane for five days at room temperature in accordancewith some embodiments.

FIG. 41 presents a flowchart illustrating a process of preparing alithium metal electrode for an electrochemical energy storage device inaccordance with some embodiments.

FIG. 42 presents a flowchart illustrating a process of preparingelectrodes for an electrochemical energy storage device in accordancewith some embodiments.

FIG. 43 shows conductivity vs. temperature data of a compressed gassolvent (without mixing) and two mixtures of various compressed gassolvents with 0.02 M TEABF₄ salt in accordance with some embodiments.

FIG. 44 shows measurements of cyclic voltammetry curves of improvedpotential window for two electrolytes composed of 0.1 M1-Butyl-3-methylimidazolium Bis(trifluoromethylsulfonyl) Imide (BMITFSI)salt in compressed gas solvent difluoromethane and liquidous propylenecarbonate in accordance with some embodiments.

FIG. 45 illustrates an exemplary electroplating device structure fordepositing difficult-to-deposit metals or alloys, using compressed gassolvent-based electrolytes having lowered reduction potential inaccordance with some embodiments.

FIG. 46 shows a cyclic voltammogram of the electroplating of titanium byreduction of TiCl₄ at a platinum metal surface in an compressed gaselectrolyte composed of electrolyte comprising of 0.1 M BMITFSI, 0.1 MTiCl₄ in difluoromethane in accordance with some embodiments.

FIG. 47 presents a flowchart illustrating a process of electroplatingdifficult-to-deposit metals or alloys using compressed gas electrolytesas an electroplating bath in accordance with some embodiments.

FIG. 48 illustrates an exemplary higher-voltage supercapacitor deviceincluding electrochemical double layer capacitors and using compressedgas electrolytes having wider potential windows in accordance with someembodiments.

FIG. 49 shows three types of higher-voltage supercapacitor devices usingcompressed gas solvent-based electrolytes having wider potential windowsin accordance with some embodiments.

FIG. 50 illustrates a schematic of such a LIB energy storage deviceincorporated within pressure chamber structure, with battery charging vsdischarging reactions illustrated in accordance with some embodiments.

DETAILED DESCRIPTION Introduction

It is generally agreed that a limiting factor to further extendelectrochemical capabilities of electrochemical energy storage devices,such as rechargeable Lithium (Li)-ion batteries (LIB) andelectrochemical double layer capacitors (EDLC) is the electrolyte, andintense efforts are being made to improve these systems by expanding thepotential window and conductivity over a wide temperature range.Properties that make up a good solvent for electrolytes (e.g., solventviscosity, permittivity, reduction and oxidation potentials,conductivity, etc.) are well-known and studied for numerous solvents.However, potential windows, defined as the potential difference betweenwhich significant oxidation and reduction current occurs, are typicallylimited to less than ˜4.5 V for the existing electrolyte-based systems.Ionic liquid-based electrolytes offer a promising approach toelectrochemical systems but are still difficult to handle, manufactureand often do not perform as well as traditional organic electrolytes.High energy density cathodes that have been developed for nextgeneration Li-ion batteries have yet to be implemented because of thelack of a suitable electrolyte system. Electrochemical double layercapacitors are similarly limited in their energy density due to limitedpotential window of the electrolytes.

The vast majority of research efforts on new electrolytes target systemsusing chemicals that are liquid at room temperature and atmosphericpressure, herein referred to as “liquid solvents.” While convenient towork with, these liquid solvents may not offer the best properties. Theuse of low molecular weight compressed gas solvents based onhydrofluorocarbon solvents molecules can be promising candidate solventsin next generation electrolytes. These solvents generally exhibit highoxidation resistance, due to the highly electronegative fluorine groupsof these hydrofluorocarbon molecules. Optimization of the conductivityof these compressed gas solvent systems, which would enable utilizationof these electrolytes in batteries and electrochemical double layercapacitors, has not been done. According to some embodiments of thispatent disclosure, new data obtained has shown that these electrolytesystems can actually be made highly conductive over a surprisingly broadrange of temperatures and enable the use of these novel solvents in nextgeneration, significantly higher-capacity energy storage devices.

Large capacity energy storage devices such as Li-ion batteries orsupercapacitors are important devices essential for modern engineeringand communications devices as well as consumer markets. These devicesare described below.

Supercapacitors (or electrochemical capacitors) are made up of twoelectrodes physically separated by an ion-permeable membrane (oftencalled a separator), immersed in an electrolyte which electricallyconnects the two electrodes (i.e., cathode and anode). When a voltage isapplied and the electrodes are polarized, ions in the electrolyte formelectric double layers of opposite polarity to the electrode's polarity.Thus, a positively polarized electrode will have a layer of negativeions forming at the interface between electrode and electrolyte. Forcharge-balancing, a layer of positive ions adsorb onto the negativelayer. For the negatively polarized electrode, the opposite situation isdeveloped.

Typically, the energy density of batteries increases with the operatingvoltage, and energy stored electrochemically inside the electrode. Insupercapacitors (also referred to as “electrochemical double-layercapacitors” or sometimes as “ultracapacitors”), the energy density isproportional to capacitance times voltage squared, i.e., E=(½)CV², andenergy is stored in the electrostatic attraction between oppositecharges in the electrode and in the electrolyte. Therefore, a higheroperating voltage is important for achieving higher power in energystorage devices such as supercapacitors and batteries. With a greaterdemand for increased energy densities in electrochemical energy storagedevices, significant improvements can be made by increasing the voltageratings of such devices.

Based on electrode design, three types of supercapacitors are oftenused. (1) Electrochemical double-layer capacitors (EDLC) typically usecarbon electrodes or related materials. EDLCs exhibit much higherelectrostatic double-layer capacitance than electrochemicalpseudocapacitance. (2) Electrochemical pseudocapacitors typically usemetal oxide or conducting polymer electrodes. (3) Hybrid capacitors haveasymmetric electrodes, for example, one electrode exhibiting mostlyelectrostatic capacitance while the other electrode showing mostlyelectrochemical capacitance.

Supercapacitors have energy densities that are approximately one tenthof conventional batteries, but with fast charge/discharge cycles, theirpower density can be 10 to 100 times greater that of the batteries. Sucha higher power density can be useful, for example, for startingautomobile engines. Acetonitrile based electrolytes are advancedelectrolytes for EDLC supercapacitors, but they are often flammable andcan release cyanide gas upon ignition. Consequently, acetonitrile basedelectrolytes are not preferred for general automotive applications.Propylene carbonate is considered a good all round solvent, but has alimitation of minimum operating temperature of −25° C. Otherelectrolytes being developed use ionic liquids. Such electrolytes arevery expensive to manufacture, and their low temperature performancetends to be very poor.

The energy density of both Li-ion batteries and supercapacitors isstrongly dependent on operating voltage. Additionally, there are someother important aspects that require innovative new concepts to overcomethe current barriers. The disclosed compressed gas solvent-basedelectrolytes provides solutions to overcome these barriers, which aredescribed below.

(1) A major contributing factor to the voltage limitation ofelectrochemical energy storage devices is the stability of theelectrolyte's solvent. At high oxidizing or reducing voltages, thesolvent may break down and increase resistance, and as a result a lossof charge storage capability (capacity), gassing and device end of lifemay be reached. Hence, improving the stability of such devices is highlydependent on the electrolyte system used, and the disclosed compressedgas solvent-based electrolyte system enables a higher voltage operationof the electrochemical energy storage devices.

(2) The ionic conductivity of electrolytes is often lowered by highlyviscous solvents or with relatively high melting point solvents. Hence,identifying a solvent, or a mixture of solvents having a low viscosityand a low melting point is important to improve the ionic conductivityof electrolyte systems. The disclosed compressed gas solvent-basedelectrolyte system offers improved ionic conductivity.

(3) The solid-electrolyte-interface (SEI) is known to be an importantcomponent in common electrochemical energy storage devices, of which thesolvent in the electrolyte plays an important role. The SEI is acomplex, yet very thin layer (e.g., 10-100 nm in thickness) that formson the electrode surface from the decomposition products from thebattery's electrolyte, often due to side reactions caused mainly byreduction or oxidation of solvents at the surface. SEI is very sensitiveto water and oxygen, and battery degradation with time and cycles isoften attributed to the properties of the SEI layer. Identifyingsolvents that play a beneficial role in the SEI layer formation,producing SEI layers that are less detrimental to the batteryoperational cycles and long term battery stability are desired. Thedisclosed compressed gas solvent-based electrolyte system offers apossibility of more stable SEI layer formation.

(4) Many electrochemical device applications such as supercapacitorsrequire a high surface area electrode with nanopores that are ofteninaccessible to the electrolyte due to high surface tension, trapped gasor generated gas within the electrode. An electrolyte with improvedaccessibility to these nanopores is beneficial to the overall systemperformance. The disclosed compressed gas solvent-based electrolytesystem offers an easier penetration of electrolytes into nanoporoussurfaces by virtue of the higher pressure employed in the compressed gassolvent-based devices.

(5) Electrodeposition of difficult-to-electroplate metals and alloyssuch as Ti, Al, Si, and W can be enabled with larger potential windowsin electrochemical systems, and therefore it is desirable to find asolvent and electrolyte compositions that can enable electroplating ofsuch metals for a myriad of industrial applications, which also includeimproved redox electrochemistry and chemical sensing. Enabling ofelectrodeposition of semiconductors such as Si can offer significantmanufacturing and economic advantages for the electronics industry.Enabling of electrodeposition of aluminum, titanium, tungsten and theiralloys can have significant industrial and economic impact toward easierand inexpensive surface passivation (e.g., via anodization coatingformation for protective or decorative surfaces), corrosion resistance,wear resistance, and environmental cleaning (e.g., in the case ofutilizing the advantageous effect of titanium or titanium oxide surfacecoating for enhanced decomposition of toxic materials or for waterpurification). The disclosed technology enables electroplating orsensing with higher electrochemical potential windows.

The disclosed technology can increase the potential window of theelectrolyte, improve ionic conductivity over a wide temperature range,improve the SEI layers, and improve electrolyte accessibility tonanopores, all of which can be very useful in electrochemicalapplications such as batteries, supercapacitors, electroplating,chemical sensing and common reduction-oxidation electrochemistry.

Overview

Disclosed are novel and advantageous electrolytes, techniques formaking, structures and devices using such electrolytes, which are basedon compressed gas solvents in combination with metal-ion containing saltand/or non-metal-ion containing salt.

In the examples in this document, a compressed gas solvent-basedelectrolyte or “compressed gas electrolyte” is a mixture electrolytethat includes a compressed gas solvent portion and a salt portion whichare mixed together under a pressurized condition to form the compressedgas electrolyte. The compressed gas solvent is made of a solventmaterial typically in gas phase under normal atmospheric conditions,i.e., at a pressure of 100 kPa, or one atmosphere, and at the ambient orroom temperature (e.g., a temperature around 293.15 K). In manyimplementations, when used as solvent in the compressed gas electrolyte,this solvent material is pressurized at a pressure much higher than oneatmospheric pressure, for example, at a pressure from 100 psi to 500psi, so that the solvent material is in a liquid phase (i.e., thecompressed gas solvent) to provide a suitable solubility for salts tocreate a conductive electrolyte. To maintain the pressure so that thesolvent material stays in the liquid phase, the compressed gaselectrolyte is generally placed inside a sealed container which caneffectuate a high pressure. In other implementations, the solventmaterial for the compressed gas electrolyte may be in a phase other thanthe liquid phase. For example, in some circumstances, the compressed gassolvent can in a super-critical phase in the compressed gas electrolyte.More specifically, under proper temperature and pressure conditions, thesolvent material forms a super-critical phase to provide a suitablesolubility for salts to create a conductive electrolyte, typically abovethe solvent material's critical temperature and critical pressure,commonly known as “critical points.” In various applications, such adesired solvent material for the compressed gas solvent may exhibit arelatively high dielectric constant, a relatively low viscosity, andrelatively low boiling point and melting point. Some of the exemplarysolvent materials for the compressed gas solvents include:trifluoromethane, difluoromethane, fluoromethane, tetrafluoroethane,pentafluoroethane, among others. For example, difluoromethane can havethe following properties: melting point of −136° C., a boiling point of−52° C, a viscosity at 25° C. of 0.11, a dielectric constant at 25° C.of 15, and a dipole moment of 1.9.

Compressed gas solvent-based electrolytes can have wide electrochemicalpotential windows, high conductivity, low temperature capability, highoxidation resistance, and high pressure solvent properties. Examples ofa class of compressed gases that can be used as solvent for electrolytesinclude hydrofluorocarbons, in particular fluoromethane,difluoromethane, tetrafluoroethane, pentafluoroethane, among others.Other classes of compressed gases may be used as solvent forelectrolytes as well, e.g., hydrofluoroolefins,hydrofluorochlorocarbons, chlorofluorocarbons, among others. In someembodiments, compressed gas solvents having a composition which givesrise to high electronegativity (e.g., fluorine, chlorine, oxygen,nitrogen, etc.), high polarity, and oxidation resistance are desirable.Generally, any compressed gas having sufficiently high relativepermittivity and suitable solubility for salts to create a conductiveelectrolyte may be used. Thus, non-fluorine-containing compressed gassolvents such as those based on chlorine, or a compressed gas solventshaving two or more mixed gases are also included in this patentdisclosure. Applications of the disclosed compressed gas-basedelectrolytes include electrochemical energy storage, electroplating andelectrochemical sensing, among others.

Also disclosed in this patent document are electrochemical energystorage devices such as battery structures and supercapacitor structuresthat use compressed gas solvent-based electrolytes, and techniques forconstructing such energy storage devices. Also techniques forelectroplating difficult-to-deposit metals or alloys using compressedgas electrolytes as an electroplating bath are disclosed.

Typically, electrolytes used in electrochemical energy storage devices,such as battery and supercapacitors, are composed of various salts andsolvents. These solvents are typically in liquid phase under normalatmospheric conditions, which typically defined as a pressure of 100kPa, or one atmosphere, and a temperature of 293.15 K, or roomtemperature. Some exceptions to this general rule include, most notably,ethylene carbonate, which is in solid phase under normal atmosphericconditions, but typically used as a mixture with one or more co-solventsto form a liquid phase.

In some embodiments of this patent disclosure, electrolytes based oncompressed gas solvents mixed with various salts, referred to as“compressed gas electrolytes”, and devices comprising such compressedgas electrolytes are disclosed. The disclosed compressed gaselectrolytes can have wide electrochemical potential windows, highconductivity, low or high temperature operation capability, highoxidation resistance, and beneficial high pressure solvent or beneficialsolid electrolyte interfaces (SEI) forming properties.

In some embodiments, the compressed gas solvent component of theproposed compressed gas electrolyte includes a chemical having a vaporpressure greater than atmospheric pressure of 100 kPa at roomtemperature of 293.15K, or having a boiling point temperature less thanroom temperature. In various embodiments, four phases of a givencompressed gas solvent may be used: solid phase, liquid phase, gasphase, and super-critical phase. The use of a mixture of these phases isnot excluded from this patent disclosure. For example, a compressed gassolvent component in liquid phase may be at least 50%, preferably atleast 80% of the total weight of the electrolyte weight, while othercomponents of solid phase, gas phase, supercritical phase or theirmixture can be less than 50%, preferably less than 20% in weight. Thesolid phase can be used when the compressed gas solvent is undertemperature and pressure conditions causing the solvent material tocondense into a solid phase, typically below the compressed gassolvent's freezing point. Similarly, the liquid phase can be used whenthe compressed gas solvent is under temperature and pressure conditionscausing the solvent material to condense into a liquid phase, typicallyabove the compressed gas solvent's freezing point. Furthermore, the gasphase can be used when the compressed gas solvent is under temperatureand pressure conditions causing the solvent material to form a gasphase, typically above the solvent's boiling point. Moreover, thesuper-critical phase can be used when the compressed gas solvent isunder temperature and pressure conditions causing the solvent materialto form a super-critical phase, typically above the solvent's criticaltemperature and critical pressure, commonly known as “critical points.”While the disclosed compressed gas electrolyte may use the solvent inany of these four phases, in some implementations, it is preferable touse the solvent in the liquid or super-critical phase to allow fordesirable electrolyte properties. In some implementations, it is morepreferable to use the solvent in the liquid phase.

When used in the liquid phase, the compressed gas solvent at a giventemperature is typically under compressive pressure equal to, or greaterthan the compressed gas solvent's vapor pressure at that temperature. Attemperatures below the compressed gas solvent's boiling point, thispressure will typically be below atmospheric pressure. At temperaturesabove the compressed gas solvent's boiling point, this pressure willtypically be greater than atmospheric pressure. At pressures greaterthan atmospheric pressure, a rigid container is typically used tomaintain a sufficiently high pressure to keep the compressed gas solventin the liquid phase. Hence, according to some embodiments of this patentdisclosure, the pressures required to maintain the liquid phase can beapplied either by the compressed gas solvent's own vapor pressure or byan externally applied pressure, or a combination of both of the above.Furthermore, the compressed gas solvent may be composed of one chemicalor multiple different chemicals, where at least one of the composingchemicals is a compressed gas solvent, according to some embodiments ofthis patent disclosure. Moreover, one or more types of compressed gassolvents can be mixed with any number of solid or liquid chemicals toform a compressed gas solvent mixture. As commonly known, mixtures ofvarious chemicals may greatly change the boiling, freezing or criticalpoints associated with individual component of the mixture. Furthermore,the compressed gas solvent can also be made of mixtures that are liquidunder atmospheric conditions if at least one of the components in themixture is a compressed gas solvent. In some embodiments, to form thedisclosed compressed gas electrolyte, any of the above-describedcompressed gas solvents or compressed gas solvent mixtures is mixed withone or more types of salts. The compressed gas electrolyte can then beused in various of devices as described in more detail below.

Examples of a class of chemicals that can be used as solvent forcompressed gas electrolytes include fluorinated hydrocarbon alkanes, inparticular fluoromethane, difluoromethane, trifluoromethane,fluoroethane, 1,1-difluoroethane, 1,2-difluoroethane,1,1,1-trifluoroethane, 1,1,2-trifluoroethane, 1,1,1,2-tetrafluoroethane,1,1,2,2-tetrafluoroethane, pentafluoroethane, 1-fluoropropane,2-fluoropropane, 1,1-difluoropropane, 1,2-difluoropropane,2,2-fluoropropane, 1,1,1-trifluoropropane, 1,1,2-trifluoropropane,1,2,2-trifluoropropane, and isomers of the above, and other similarlonger chained fluorinated hydrocarbon alkanes.

Other chemicals that can be used as solvent for electrolytes includefluorinated hydrocarbon alkenes such as fluoroethylene,cis-1,2-fluoroethylene, 1,1-fluoroethylene, 1-fluoropropylene,2-propylene, and isomers of the above and other similar longer chainedfluorinated hydrocarbon alkenes. Moreover, fluorinated hydrocarbonalkynes may be used, including fluoroethyne or other fluorinated ethynewith an extended radical group. Furthermore, a class of chemicals thatcan be used as solvent for electrolytes may be similar in structure toany of the above-described compressed gas solvents but having adifferent halogenated component such as chlorine, bromine or iodine.Moreover, another class of chemicals that can be used as solvent forelectrolytes may have a dissimilar structure to above-describedcompressed gas solvents, such as ammonia or nitrous oxide, molecularoxygen, molecular nitrogen, carbon dioxide, carbon monoxide, hydrogenfluoride or hydrogen chloride. In some embodiments, a disclosedcompressed gas solvent associated with some or all of the followingproperties: a relatively high dielectric constant, high polarity, highresistance to reduction and oxidation, nontoxic, non-flammable, and lowenvironmental impact. Generally, any compressed gas solvent that cansolubilize salts to form an ionically conductive electrolyte solutionmay be used according to some embodiments of this patent disclosure.

Solvents of high oxidation resistance are often required inelectrochemical studies or applications. Addition of highlyelectronegative fluorine to common hydrocarbons often creates a polarsolvent capable of solubilizing salts and increases solvent oxidationresistance. The higher oxidation resistance may allow for applicationsas a solvent in high voltage batteries, high voltage electrochemicalcapacitors, chemical sensing and common reduction-oxidationelectrochemistry.

Conventional electrochemical energy storage devices, such as batteriesor electrochemical double-layer capacitors (also known as“supercapacitors”) using liquid solvents are well known to those skilledin the art. Generally, such an energy storage device is comprised of twoelectrically conducting electrodes, each of the electrodes furthercomprises a current collector and an active material layer, which iscoated on the inner surface of the current collector. Supercapacitorstypically have electrodes comprised of activated-carbon based materials,such as porous carbon, which have a high surface area per unit volume orper unit mass. Batteries typically have electrodes composed of materialallowing for intercalation of ions into the electrode material. In bothbatteries and supercapacitors, typically the two conducting electrodesare immersed into a conductive solution, i.e., the electrolyte. Theelectrodes are also separated by an electrically non-conductingseparator which typically has porous structure to allow passage of ionswithin the electrolyte.

For example, FIG. 1 illustrates schematics of (A) an exemplarylithium-ion battery and (B) an exemplary electrochemical double-layercapacitor (supercapacitor) including two charged electrodes separated bythe electrolyte. Note that in the supercapacitor, the electrolytefurther comprises anions (negatively charged ions) and cations(positively charged ions) solvated in a solvent.

The power capability of electrochemical storage devices is dependent onthe conductivities of many of its components, including the electrolyte.FIG. 2 shows a schematic of a common supercapacitor device andequivalent resistances coupled in series, each corresponding to arespective component of the supercapacitor device. It is generallyaccepted that electrolyte solvent viscosity is one of the determiningfactors in the conductivity of the electrolyte. Typically, the viscosityis also related to the temperature of the solvent. The conductivity ofthe electrolyte system typically drops rapidly when the operatingtemperature cools down and reaches the freezing point of the electrolytesystem. Consequently, improving the power capability of electrochemicalstorage devices is highly dependent on the viscosity and freezing pointof the electrolyte system used in these devices.

It should also be noted that in some electrochemical storage devices,such as supercapacitors, energy storage is partly determined by accessto nano-sized pores in the active material layers. Many electrolytesystems do not have access to these pores because of high surfacetension between the electrolyte and electrode surface or trapped airwithin the pores, limiting the possible energy density of the device. Adesirable electrolyte would have low surface tension and allow access tothe micro pores on an electrode surface.

Solvents of high oxidation resistance (such as dichloromethane oracetonitrile) are often desired for more practical electrochemicalapplications. Typically, solvents of high oxidation resistance containatoms of high electronegativity. The addition of, or substitution ofother highly electronegative elements with, fluorine in these solventsas described in this patent disclosure typically lowers the boilingpoint significantly, often rendering the solvent gaseous at roomtemperature. However, the addition of the highly electronegativefluorine to these solvents makes them highly oxidation resistant. Theincreased oxidation resistance widens the potential window of theelectrolyte and can be very useful in electrochemical applications suchas batteries, electrochemical capacitors, chemical sensing and commonreduction-oxidation electrochemistry.

Various embodiments of this patent document disclose electrolytes basedon one or more types of compressed gas solvents mixed with one or moretypes of salts to form an ionically conducting mixture, referred to as“compressed gas solvent-based electrolytes” or simply “compressed gaselectrolytes,” and devices comprising such compressed gas electrolytes.The disclosed compressed gas electrolytes can have wide electrochemicalpotential windows, high oxidation resistance, high conductivity, low orhigh temperature operation capability, and beneficial high pressuresolvent or SEI forming properties.

FIG. 3 presents a table listing detailed properties of commonlyavailable solvents compared with a proposed compressed gas solvent,difluoromethane, which is a fluorinated compressed gas solvent inaccordance with some embodiments. As can be seen in FIG. 3, thecompressed gas solvent shows significantly lower viscosity, potentiallyallowing for higher charge carrier, or ion mobility, thereby leading tohigh ionic conductivity when used to form salt solutions. Notably, themelting point of the compressed gas solvent is significantly lower thanthat of those common liquid solvents. This property allows for highionic conductivity and device operation down to very low temperatures,which is not available to common liquid solvents. Some embodiments ofthis patent disclosure utilize this property to construct improvedenergy storage devices, perform wider-potential-window electrochemicaldeposition and electrochemical sensing.

FIG. 4 presents a table listing detailed properties of some of theproposed compressed gas solvents which may be good candidates forwider-potential-window electrochemical energy storage devices, andplating and sensing application, in accordance with some embodiments. Ascan be seen in FIG. 4, the table includes vapor pressures of theproposed compressed gas solvents at room temperature. In more detail,FIG. 5 shows a plot comparing vapor pressures of the compressed gassolvents listed in FIG. 4 over a wide temperature range in accordancewith some embodiments. In some embodiments, a compressed gas solventwith relatively higher vapor pressure in a group of candidate compressedgas solvents is selected to facilitate achieving higher ion access tonano pores in highly porous electrodes, a property which can bebeneficial to the energy storage device operation.

The solubility of salts in some proposed compressed gas solvents may belimited due to typically low dielectric constants and molecular polarityof these solvents. FIG. 6 and FIG. 7 illustrate schematically exampleswhich salt ions can be solvated in a lower dielectric solvent, but alsocan form higher solvated ion aggregates in the lower dielectric solvent.More specifically, FIG. 6 illustrates an example of salt ions (with morenegatively charged ions 30 than positively charged ions 31) solvated insolvent molecules 32 to form negative charge carriers 33 including botha solvated single ion and solvated ion aggregates. FIG. 7 illustrates anexample of salt ions (with more positively charged ions 31 thannegatively charged ions 30) solvated in solvent molecules 32 to formpositive charge carriers 34 including both a solvated single ion andsolvated ion aggregates. While larger in size and lower in mobility,these solvated ion aggregates can still contribute to the ionicconductivity of the solution.

FIG. 8 shows conductivities vs. temperature plots of various electrolytesystems containing various solvents and the same salt, e.g., 0.02M ofTBAPF6 salt, in accordance with some embodiments. As shown in FIG. 8,the compressed gas solvent difluoromethane shows superior lowtemperature capability and significantly higher conductivity than itsliquidus halogenated counterpart, liquid dichloromethane. Thefluorinated compressed-gas-solvents proposed in the patent documentdisplay a remarkably high electrolytic conductivity when mixed withcommonly used tetra-alkyl-ammonium salts as shown in the data plot.Although dichloromethane and difluoromethane are closely relatedstructurally with a simple substitution of chlorine for moreelectronegative fluorine, there are significant differences in theelectrolytic conductivity. Difluoromethane shows more than an order ofmagnitude higher conductivity over dichloromethane. Furthermore,difluoromethane shows superior conductivity over acetonitrile attemperatures below ˜20° C., while showing exceptional conductivity aslow as −60° C. The non-linear shape to the conductivity vs. temperaturecurve for the difluoromethane compressed gas electrolyte is thought toarise from the changing viscosity of the compressed gas solvent and ionaggregation effects over temperature. Hence, in some embodiments,fluorinated compressed-gas-solvents difluoromethane and related solventsare desirable solvents for constructing higher conducting electrolytesfor electrochemical energy storage devices.

In the discussion below, the following chemical acronyms may be used:TEA=tetraethylammonium, TBA=tetrabutylammonium, ClO4=perchlorate,BF4=tetrafluoroborate, PF6=hexafluorophosphate,TFSI=bis-trifluoromethanesulfonimidate, EMI=1-ethyl-3-methylimidazolium,and LiTFSI=lithium bis-trifluoromethanesulfonimide, among other.

FIG. 9 shows conductivities vs. temperature plots of compressed gassolvent difluoromethane with 0.02 M of various salts forming conductivecompressed gas electrolyte systems in accordance with some embodiments.As shown in FIG. 9, electrolytes based on certain salts provide higherconductivities at various temperatures in the same compressed gassolvent medium.

FIG. 10 shows conductivities vs. temperature plots of compressed gassolvent difluoromethane with different concentrations oftetrabutylammonium hexafluorophosphate (TBAPF6) salt in accordance withsome embodiments. Note that an increase in conductivity is associatedwith an increasing concentration of the salt. Hence, the conductivityvalues can be further improved by adjusting, e.g., increasing the amountof salt as needed for batteries or supercapacitor applications.

FIG. 11 shows conductivities vs. temperature plots of electrolytesystems containing fluoromethane and fluoroethane compressed gassolvents and lithium bis-trifluoromethanesulfonimide (LiTFSI) salt inaccordance with some embodiments. These electrolyte systems can be usedin lithium battery electrochemical energy storage devices operated withcompressed gas solvent-based electrolytes. These two compressed gassolvents, fluoromethane and fluoroethane, exhibit desirable stability,sufficient dielectric properties and relatively low global warmingpotential (GWP).

FIG. 12 presents a table listing stability, dipole moment and GWP ofvarious proposed compressed gas solvents including fluorine-containingsolvents in accordance with some embodiments. The GWP is a relativemeasure of how much heat a gas identified to be a greenhouse gas trapsin the atmosphere, relative to CO₂ (carbon dioxide), and hence the lowerthe GWP value is, the better and less environmentally hazardous the gasis. As shown in the table, the GWP of fluoromethane is 92, which is inthe same order of magnitude as the GWP of 25 for methane, while the GWPof fluoroethane (one of the hydrofluorocarbon compressible gas in thisinvention) is only 12.

In some embodiments, the desirable energy storage devices containcompressed gas solvent having the GWP value desirably less than 1,000,preferably less than 100, and even more preferentially less than 20. Insome other embodiments, the energy storage devices containing compressedgas solvent is well sealed so that the solvent gas is substantially notleaked into the air, desirably less than 10%, preferably less than 5%,and even more preferably less than 1% of the solvent content per year.

FIG. 13 shows cyclic voltammetry curves of electrolyte systems based onboth dichloromethane and difluoromethane solvents containing 0.02 MTEABF4 salt under a scan rate of 50 mV/s at room temperature inaccordance with some embodiments. As can be seen in FIG. 13, thoughsimilar in structure, the high electronegativity of the fluorine givesrise to higher oxidation resistance to the solvent and therefore shiftsthe oxidation potential (i.e., where the current reduces to zero)approximately 1 V higher when compared to the fluorine-freedichloromethane solvent. This properties can be beneficial in manyelectrochemical devices requiring a more oxidation resistant solvent,including batteries, supercapacitors, electroplating systems andsensors. FIG. 14 shows cyclic voltammetry curves of difluoromethanecontaining 0.02 M of different salts with a scan rate of 50 mV/s at roomtemperature in accordance with some embodiments. This plot shows thesalt used may have the effect of increasing, decreasing, or shifting thepotential window of the compressed gas electrolyte, which exhibitsdesirable trends for higher potential windows, and higher energycapacity energy storage devices. FIG. 15 shows cyclic voltammetry curvesfor different solvent systems using LiTFSI or LiPF6 based salt with ascan rate of 100 mV/s at room temperature in accordance with someembodiments. It can be observed that difluoromethane based system hasrelatively high oxidation potential compared to other solvent systems,up to approximately 6 V vs. Li/Li+, as shown by the rapid increase incurrent at 6 V vs a lithium reference. This value shows a trend ofdesirably widened potential window, according to some embodiments ofthis patent disclosure, by employing compressed gas solventelectrolytes. Some oxidation current below this voltage is thought to bedue to impurities in the solvent.

In some embodiments, the electrochemical energy storage device based onLi-ion battery system containing compressed gas electrolyte exhibitswider potential window of at least 4.5V, preferably at least 4.8V, evenmore preferentially at least 5.2V. In some other embodiments, theelectrochemical energy storage device based on supercapacitor structurecontaining compressed gas electrolyte exhibits wider potential window ofat least 2.8V, preferably at least 3.0V, even more preferentially atleast 3.3V.

If the liquid volume of the compressed gas solvent expands withtemperature and at a certain temperature not allowed to further expand,then there is an isochoric (i.e., constant volume situation, or “volumeconstrained”) increase in pressure on the system above the solvent'snormal vapor pressure. FIG. 16 shows measurements of pressure insidepressure vessel containing volume of solvent for both isochoric increasein pressure in a volume constrained system and a purely vapor pressurebased volume unconstrained system in accordance with some embodiments.As can be seen, in the volume constrained system (filled circles) whenthe solvent is not allowed to increase further in volume, the pressureincreases rapidly with increasing temperature. Common compressed gassolvents may suffer from lower conductivity at higher temperatures dueto lower ion mobility caused by lower dielectric constant of the solventand higher ion-ion interaction.

FIG. 17 shows conductivity and pressure vs. temperature measurement ofdifluoromethane solvent containing 0.1 M TBAPF₆ salt under isochoricincrease in pressure of the solvent system in accordance with someembodiments. As can be seen in FIG. 17, in this system, thedifluoromethane solvent is shown to have a sharp increase in pressuredue to isochoric increase in solvent pressure at ˜48° C. and theconductivity curve is shown to have a sharp change in conductivity(i.e., rapid slowdown of conductivity decreasing rate) at the sametemperature. The sudden change in conductivity is thought to be due toan increase in the local dielectric constant of the compressed gassolvent, which may decrease the ion-ion interaction and increase ionicconductivity. This technique of utilizing isochoric increase in pressuremay be optimized to provide a higher conducting electrolyte over a widetemperature range, or at least minimize the loss of conductivity athigher temperature. Hence, this described isochoric increase in pressureand associated conductivity enhancement is another aspect of disclosedtechnology which can be exploited for improvement of battery andsupercapacitor performances through optimal design and pressure controlin the compressed gas solvent chamber.

FIG. 18 illustrates an ionically conducting electrolyte composed of amixture of salt and solvent inside an pressurized housing to form anelectrochemical cell 40 in accordance with some embodiments. As can beseen in FIG. 18, the ionically conducting electrolyte includes negativecharge carriers 33 and positive charge carriers 34 of one or more typesof salt surrounded by solvent molecules 32 of a compressed gas solvent.This compressed gas solvent is in a gas phase and has a vapor pressureabove an atmospheric pressure at a room temperature. The electrochemicalcell 40 also includes a pressured housing 20 which encloses solventmolecules 32, negative charge carriers 33 and positive charge carriers34, and is structured to provide a pressurized condition to thecompressed gas solvent. The electrochemical cell 40 also includes a pairof conducting electrodes in contact with the ionically conductingelectrolyte. The pair of conducting electrodes further includes anegative current collector 10, negative electrode material 11, ionicallyconducting porous separator 12, positive electrode material 13, andpositive current collector 14. The electrode materials 11 and 13 mayvary among different battery and electrochemical capacitor systems, butthey are typically materials which allow high quantity of lithiumintercalation for use in lithium batteries and high surface area carbonelectrodes in electrochemical capacitors.

Because the performance of electrochemical devices such assupercapacitors and Li-ion batteries are dependent on total surface areaof the electrodes, it is highly desirable to incorporatelarge-surface-area structures, e.g., by utilizing nanostructured anodesand cathodes. In addition to the increased total surface area,nanostructured electrode materials can also offer more robust mechanicalproperties to accommodate strains and stresses, for example, withsignificant volume changes occurring as Li atoms are intercalated in andout of the electrodes during charge-discharge cycling. In some exemplaryelectrochemical devices based on compressed gas solvent electrolytes,the desired electrode structures have a large surface area, with thesurface area being at least 100 m²/g, preferably at least 500 m²/g, andeven more preferably at least 2,000 m²/g. The surface areas of theelectrode structures can be determined by well-knownBrunauer-Emmett-Teller (BET) surface area analysis utilizing themeasurements of gas adsorption. In some embodiments, an exemplaryelectrochemical device of FIG. 18 use an electrochemically activepolymer or metal oxide for one or both negative electrode material 11and positive electrode material 13.

In the embodiments where nanostructured electrode configuration isdesired, the exemplary supercapacitors and batteries can optionally havenanostructures selected from nanofibers, nanopillars, nanoparticleaggregates, nanoporous structures, or a combination of the above, andhaving a feature dimension of diameter or pore-size less than 500 nm,preferably less than 50 nm, and even more preferably less than 5 nm. Insome embodiments, the preferable dimension is about 1 nm, with thepore-size being made similar in size to that of the unsolvated ions inthe electrolyte.

FIG. 19 illustrates an electrochemical electrode assembly 8 beingpackaged inside a device package to form an electrochemical cell 50 inaccordance with some embodiments. As can be seen in FIG. 19, theelectrochemical electrode assembly 8 comprising anode current collector10, anode electrode material 11, separator 12, cathode electrodematerial 13, and cathode current collector 14. The electrochemicalelectrode assembly 8 is placed inside a device package to make handlingeasier. The device package further includes a negative (anode) terminal15 and a positive (cathode) terminal 16 electrically coupled to currentcollectors 10 and 14 through a mechanical device housing 20. Theelectrical terminals 15 and 16 can pass through electrically insulatingor conducting feedthroughs 17. The housing 20 may be either metallic orinsulating or metallic with an insulating inner and or outer surface.When used with compressed gas solvents, it is desirable that the housing20 be rigid enough to safely contain the high pressure electrolyte(i.e., housing 20 being a high pressure housing). Also within the devicepackage there is a port 18 through which compressed gas solvent orcompressed gas electrolyte can be filled into the device. In someembodiments, there is also a second port through which it is possible topurge the electrochemical cell 50, or to completely fill the cell withno trapped gas. Also within the electrochemical cell 50 there can be asensor or group of sensors 19 to determine the environment andconditions of the cell assembly such as pressure, temperature, solventlevel, voltage, charge capacity, or other quantities that may be usefulto monitor.

FIG. 20 presents a flowchart illustrating a process 2000 of filling theelectrochemical electrode assembly and housing, such as the onedescribed in FIG. 19 with a compressed gas electrolyte in accordancewith some embodiments. One may first mix a compressed gas solvent and asalt into a high pressure container to form a compressed gas electrolytewith a desired concentration of salt (2002). Then the mixed compressedgas electrolyte is inserted into an electrochemical cell assemblycomprising an electrochemical electrode assembly and a high pressurehousing, thereby forming an operating electrochemical cell (2004).

FIG. 21 presents a flowchart illustrating another process 2100 offilling the electrochemical electrode assembly and housing, such as theone described in FIG. 19 with a compressed gas electrolyte in accordancewith some embodiments. In this technique, a salt is first inserted intoan electrochemical electrode assembly inside the rigid housing to form asalt loaded electrochemical electrode assembly (2102). Next, acompressed gas solvent is introduced into the salt loadedelectrochemical electrode assembly to be mixed with the salt to createthe compressed gas electrolyte inside the rigid housing, thereby formingan operating electrochemical cell (2104). Note that in both techniques2000 and 2100, introducing the compressed gas electrolyte or compressedgas solvent into the electrochemical electrode assembly may be aided bythe use of a temperature differential between the compressed gaselectrolyte or the compressed gas solvent and the respectiveelectrochemical electrode assembly.

Example #1

Multiple electrochemical cells containing compressed gas solvent basedelectrolytes created by process 2100 are assembled into batteries andelectrochemical double layer capacitors, and their properties areevaluated.

FIG. 22 shows cyclic voltammetry curves of double layer capacitordevices using different solvents containing 0.5 M TBAPF6 salt measuredat room temperature with a scan rate of 10 mV/s in accordance with someembodiments.

FIG. 22 shows cyclic voltammetry curves of two electrochemical doublelayer capacitors with equal mass electrodes using different solventscontaining 0.5 M TBAPF6 salt measured at room temperature with a scanrate of 10 mV/s in accordance with some embodiments. More specifically,one device is filled with a compressed gas electrolyte withdifluoromethane solvent and 0.5 M TBAPF6 salt, and the other device withacetonitrile solvent with 0.5 M TBAPF6 salt. The very similar shapes ofthe cyclic voltammetry curves and charge discharge currents indicatesimilar capacitances and resistances of both devices.

FIG. 23 shows a zoomed in view of the cyclic voltammetry curves in FIG.22 in accordance with some embodiments. As can be seen in FIG. 23, theacetonitrile based device begins to show high electrolyte decompositionat about 3 V while the difluoromethane device begins to show highelectrolyte decomposition at about 3.3 V. These high potential windowsindicate that these devices can operate with desirably higher workingvoltages due to the used of compressed gas solvent based electrolytes.

Higher voltage supercapacitors provide higher energy storage capabilityas the amount of energy stored is generally proportional to the squareof the operational voltage. For example, comparing with conventionalsupercapacitors having a standard 2.7V operation voltage, the disclosedcompressed gas electrolyte-based supercapacitors shown in FIG. 22operable at 3.3 V would provide [3.3²/2.7²]×100=˜50% increase insupercapacitor energy storage capability. In some embodiments, thedisclosed supercapacitors having compressed gas solvent-basedelectrolyte is capable of higher operating voltage of at least 3V,preferably at least 3.2V, even more preferably at least 3.5V, withcorresponding increase of energy storage capability of ˜23%, ˜40%, ˜68%,respectively.

Another exemplary electrochemical supercapacitor composed of compressedgas electrolyte containing difluoromethane and 0.5 M TBABF4 salt wasconstructed and tested by charging at 20 mA to 3 V, held at 3 V for onehour, and discharged to 0 V at 20 mA rate at room temperature. FIG. 24shows the resistance vs. cycle number curve of the double layercapacitor device containing difluoromethane and 0.5 M TBABF4 salt inaccordance with some embodiments. As can be seen in FIG. 24, resistancevalue increases with the number of cycles. FIG. 25 shows the leakagecurrent vs. cycle number curve of the same device containingdifluoromethane and 0.5 M TBABF4 salt in accordance with someembodiments. As can be seen in FIG. 25, resistance value decreases andstabilizes after about 300 cycles. FIG. 26 shows the capacitance vs.cycle number curve of the same device containing difluoromethane and 0.5M TBABF4 salt in accordance with some embodiments. As can be seen inFIG. 26, the capacity of the same device decreases over an increasingcycle number. The declining capacity and increasing resistance isthought to be due to impurities in the electrolyte, which is known to bedetrimental to cell performance. This exemplary supercapacitor devicewas not optimized in terms of materials, structures and assemblymethods, thus showing some increase in resistance and some currentleakage. However, the data shown in FIGS. 24-26 clearly demonstrate theprinciple that the compressed gas electrolyte-based supercapacitorfunctions in cycling operations. FIG. 27 shows the impedance spectra ofthe same device at low temperatures in accordance with some embodiments.The semi-circle portion of the curves is due primarily to the electricalresistance within the carbon electrodes and remains relatively unchangedwith decreasing temperature. The low frequency portion of the curves isprimarily a measure of the electrolyte diffusion resistance and is seento increase in resistance at lower temperature, as expected with lowermobility of ions in the electrolyte. While existing supercapacitorsbased on acetonitrile solvent have difficulties in operating attemperatures below −40° C., the disclosed difluoromethane-basedelectrolyte allows operation at temperatures as low as −70° C.

FIG. 28 shows the resistance vs. temperature curve of the same device inaccordance with some embodiments. As can be seen in FIG. 28, theresistance value increases approximately 40% from room temperature to−70° C. FIG. 29 shows increase in resistance (%) vs. temperature curvesof double layer capacitor devices using difluoromethane and acetonitrilebased electrolytes in accordance with some embodiments. As can be seenin FIG. 29, the acetonitrile-based devices start increasing inresistance considerably at −40° C. while the discloseddifluoromethane-based devices continue to operate well down to −70° C.This difference in difluoromethane-based devices is a significantimprovement over the existing devices and can be very useful inapplications requiring low temperature operation of electrochemicalenergy storage devices. The operability of supercapacitors at a lowtemperature well below −40° C. is highly desirable, for example, foroperation of automobiles, aerospace transportations, military equipmentin cold weather regions, high altitude atmosphere, and so forth.

Hence, the disclosed supercapacitor devices based on compressed gaselectrolytes enable high-performance supercapacitor operation attemperatures below −20° C., more preferably below −40° C., even morepreferably below −60° C.

Among the existing supercapacitors, acetonitrile solvent-basedsupercapacitors are considered to be state-of-the-art supercapacitors interms of the supercapacitor performance, though it is not widely usedfor critical applications due to possible flammability and other issues.FIG. 22 shows exemplary cyclic voltammetry curves of electrochemicaldouble layer capacitor devices using acetonitrile solvent vs usingcompressed gas solvent difluoromethane at room temperature. It can beseen that the two types of solvents offer comparable voltammetryperformances, indicating the feasibility of constructing supercapacitorsbased on compressed gas solvent. The tail portion of the cyclicvoltammetry curves in FIG. 22 near the higher side voltage was expandedand shown in FIG. 23. It can be seen that the compressed gassolvent-based supercapacitor exhibits cyclic voltammetry curves thatextend further toward higher voltage than the acetonitrile-basedsupercapacitor.

Example #2

A device composed of a lithium metal negative electrode and lithiumnickel manganese oxide (LMNO) positive electrode was assembled with 0.1M LiTFSI salt solvated in fluoromethane compressed gas solvent to forman electrochemical lithium-based battery device.

FIG. 30 shows a cyclic voltammetry curve of the battery device usingfluoromethane compressed gas solvent containing 0.1 M LiTFSI saltmeasured with a sweep rate of 0.03 mV/s at room temperature inaccordance with some embodiments. As can be seen in FIG. 30, the firstoxidation peak and the reduction peak indicate lithium intercalationinto and out of the LMNO positive electrode, respectively. Although theLi-ion battery structure tested was not optimized in terms ofconstruction and performance, this cyclic voltammogram demonstrates thata working Li-ion battery device using a compressed gas electrolytesystem is feasible. FIG. 31 shows an impedance spectra of the samedevice as in FIG. 30 in accordance with some embodiments. As can be seenin FIG. 31, the high frequency circle shows the impedance of what isconsidered to be a surface electrolyte interface on the positive andnegative electrode, and the medium frequency semicircle shows what isconsidered to be charge transfer resistance within the electrode. Thelow frequency straight line shows the Wardburg diffusion resistance ofions movement.

In energy storage devices such as batteries or supercapacitors, it issometimes desirable to obtain higher voltage and/or higher current byconnecting multiple individual cells in series or in parallel to form apackaged assembly. The compressed gas electrolyte-based energy storagedevices can also be assembled into more powerful systems. FIG. 32illustrates packaging multiple electrochemical cells into a singledevice assembly in accordance with some embodiments. As can be seen inFIG. 32, multiple electrochemical cells 104, each of which can beconstructed using either the process described in FIG. 20 or the processof FIG. 21, are packaged into electrochemical device assembly 110. Theassembly 110 may be composed of batteries, electrochemical capacitors,or a combination of batteries and electrochemical capacitors, which areelectrically coupled in series or in parallel.

FIG. 33 illustrates an electrical controller 111 composed of multipleenvironmental sensors and devises in accordance with some embodiments.As can be seen in FIG. 33, electrical controller 111 includes multiplesensors including a temperature sensor 112, a pressure sensor 113, acompressed gas solvent volume sensor 114. Electrical controller 111 alsoincludes addition modules including heater and cooler 115 fortemperature control, pressure generator and relief 116 for pressurecontrol, and compressed gas solvent module 117 for the solvent filllevel control within an electrochemical cell assembly. Such anelectrical controller 111 can be used to control environmentalconditions of the electrochemical cell to prolong the cell life orproduce better device performance such as power, energy or temperaturecapabilities.

FIG. 34 shows using an environmental controller 111 to monitor multipleelectrochemical device assemblies 110 in accordance with someembodiments. As can be seen in FIG. 34, an electrical controller 111,such as the one described in FIG. 33, monitors one or moreelectrochemical device assemblies 110, each of which is composed of oneor more individual electrochemical cells 104 (referring to FIG. 32). Itcan be beneficial to use a single electrical controller 111 to monitorand control multiple cell assemblies 110 to lower cost, reduce overallsize, and to increase energy efficiency of the fully packaged assembleddevice.

FIG. 35 shows multiple electrochemical device assemblies 110 can be usedto power an electrical load 119 under the control of an electricalcontroller 118 in accordance with some embodiments. In some embodiments,multiple electrochemical device assemblies 110 can be controlled byelectrical controller 118 to discharge current or energy into electricalload 119. Electrical load 119 may be used to produce work to drive anelectrical motor on a vehicle or any other application which requiresdissipated electrical energy.

Because of the unique features of the described high-pressure compressedgas electrolytes, such as the high pressure nature, it may be possiblethat the electrolyte can penetrate electrode nanopores that areotherwise inaccessible to conventional liquid solvent-basedelectrolytes. This high pressure may overcome the capillary pressurewithin the pores to allow the high surface area within nanopores tobecome more accessible.

FIG. 36 illustrates how charged carriers or ions in the high pressureelectrolyte can gain access to smaller nanopores of a high surface areacharged electrode surface by means of a higher pressure system inaccordance with some embodiments. As can be seen in FIG. 36, differenttypes of charged particles, including negatively/positively chargedcarriers and negatively/positively charged ions can penetrate into thenanoporous in nanoporous material 42 on the surface of anode or cathodecurrent collector 10 or 14. This penetrating nature is especiallybeneficial in electrochemical capacitor applications where liquidsolvent-based electrolytes may not access nanopores in the high surfacearea electrode, lowering the potential capacitance of the device. Withthe increased pressure of the compressed gas electrolytes, highercapacitance may be realized with this increased pressure. Furthermore,an external device pressure generator 116 as shown in FIG. 33 may beused to control the pressure, thereby controlling a degree of accessinto the nano pores to achieve desired device performance. In someembodiments, proposed electrochemical devices can use the supercriticalproperties of the compressed gas electrolyte. More specifically, at highenough pressures and temperatures, the electrolyte can becomesupercritical which can increase wettability to high surface areas withnano pores and can have other beneficial properties such as higher ionicconductivity.

As discussed above, the performance of electrochemical devices such assupercapacitors and Li-ion batteries are dependent on total surface areaof the electrodes, and hence it is highly desirable to incorporatenanostructured anodes and cathodes, wherein nanostructures can includenanofibers, nanopillars, nanoparticle aggregates, nanoporous structures,or a combination of the above. Within such nanostructured anodes andcathodes, a feature dimension of diameter or pore can be less than 500nm, preferably less than 50 nm, even more preferably less than 5 nm. Insome embodiments, the preferable dimension is about 1 nm. The desiredelectrode structures have a large surface area, with the surface areabeing at least 100 m²/g, preferably at least 500 m²/g, even morepreferably at least 2,000 m²/g.

Hence, the proposed electrochemical devices such as supercapacitors andLi-ion batteries enable nanopore penetration by means of high pressure,compressed gas solvent electrolytes, thereby producing improved deviceshaving well-penetrated electrolyte. In some embodiments, this highpressure is greater than the atmospheric pressure of 100 kPa, preferably10×the atmospheric pressure, or more preferably 20×the atmosphericpressure. This feature results in supercapacitors or batteries to haveat least 10% enhanced energy storage capacity, and may reach at least30% enhanced energy storage capacity as compared to an electrochemicaldevice having substantially identical nanostructured electrodes but withliquid state electrolytes instead of high pressure compressed gaselectrolytes. Furthermore, the proposed electrochemical devices caninclude a pressure controller to control the pressure of the compressedgas solvent electrolytes to achieve an optimal nanopore penetration.Moreover, the compressed gas solvent can be selected to have a highvapor pressure to facilitate higher ion access to the nanopores by atleast 10% more, preferably 30% more, and even more preferably 50% more

Solid Electrolyte Interfaces (SEI) Layers and Electrode SurfaceProtection

In Li-ion batteries, solid electrolyte interfaces (SEI) layers oftenform on the surface of the battery electrodes, primarily due to certainside chemical reactions caused by reduction or oxidation of solvents atthe surface of anodes and cathodes. Such SEI layers are not necessarilybad as they may also serve as a protective layer. The SEI layers canvary depending on the type of electrolyte and the nature of theelectrode material. Sometimes a composite inorganic-organic SEI layercan form to serve as a protective coating layer on the electrode. Anadjustable or self-healing SEI layer during charging-discharging, whichalso accommodating the associated electrode volume change can be highlydesirable. An important benefit of having such an SEI is to preventelectrolyte decomposition by means of electrically insulating theelectrolyte from the electrode surface, while allowing good ionicconduction. In some embodiments, an SEI layer may be artificiallyintroduced for its beneficial properties.

In some embodiments, using a metallic anode, such as lithium, sodium, ormagnesium anodes, allows for a significantly higher energy density. Forinstance, moving from a carbon based anode (360 mAh/g) to a lithiummetal anode (3,860 mAh/g) can lead to a large increase in energydensity. However, problems with dendrite formation often prevent the useof such metallic anodes. On repeated cycling, metallic dendrites mayform that can punch through the electrically insulating separator andelectrolyte and cause a short circuit between anode and cathode. Therehave been many attempts to mitigate formation of such dendrites. It hasbeen shown that adding lithium halides, such as lithium fluoride, to thesurface of the lithium anode may prevent dendrite formation andstabilize lithium metal cycling behavior. Furthermore, addingcompressive pressure or a polymer surface layer to the lithium metallicanode can prevent dendrite growth. In some embodiments, the undesirabledendrite formation in the high pressure compressed gas solvent-basedLi-ion battery is reduced by a factor of 2 in terms of the averagedendrite growth length, preferably by a factor of 5, even morepreferably by a factor of 10 as compared to the regular Li-ion batteryin which the solvent pressure is not high.

As is well-known, there is a spontaneous chemical reaction betweenlithium metal and the solvent and salts comprising conventionalelectrolytes due to the high reduction potential of the lithium metal.This reaction often forms many lithium containing compounds includinglithium fluoride and polymers. These compounds make up a portion of theSEI layer on the lithium metal surface. Similarly, lithium metalsubmersion into a compressed gas solvent or compressed gas electrolytecan have this same SEI layer formation effect. What is unique in thecase of some fluorinated compressed gas solvents is the strong formationof lithium fluoride or fluorocarbon polymers. More specifically, becausethere is no oxygen in these systems, aside from common contamination,the SEI layer is substantially “oxygen-free.” An oxygen-free SEI layermay have additional benefits such as higher ionic conductivity orprevention of dendrite formation. In some embodiments, dendriteformation is suppressed by 50%, or even to just one third, or evenpossible to just one tenth comparing with typical SEI layer, therebyprolonging the cyclability of the lithium metal anode.

Example #3

FIG. 37 shows example reactions and reaction products from differentcompressed gas solvents and lithium metal chemical reactions. Theseproducts are only some of the possible products from the possiblechemical reactions in accordance with some embodiments. As can be seenin FIG. 37, lithium fluoride is possibly created from reaction with thecompressed gas solvents together with a number of other materials,including strong polymerization. As an example, lithium metal wassubmerged into compressed gas solvents for five days at room temperatureand scanning electron microscope (SEM) images were then taken from themetal surface to observe different features. FIG. 38 shows the SEMimages and XPS data of surface of lithium metal after submerged intofluoromethane for five days at room temperature in accordance with someembodiments. As can be seen in FIG. 38, the SEM image (the lower rightone) shows strong cracking and what appears to be lithium fluorideformation. Elemental analysis by XPS shows a strong presence ofelemental fluoride, indicating that lithium fluoride is a possiblereaction product.

FIG. 39 shows SEM images of the surface of lithium metal after submergedinto difluoromethane for five days at room temperature in accordancewith some embodiments. As can be seen in FIG. 39, the relatively smoothlithium metal surface has what appears to be light polymerization.Moreover, FIG. 40 shows SEM images of the surface of lithium metal aftersubmerged into tetrafluoroethane for five days at room temperature inaccordance with some embodiments. As can be seen in FIG. 40, therelatively rough lithium metal surface has what appears to be strongpolymerization. The combination of lithium fluoride and polymerizationon the lithium metal surface can help preventing dendritic formation onlithium metal anodes, improving cyclability and energy density ofcurrent lithium based batteries.

Furthermore, chemical reaction with the compressed gas solvent orcompressed gas electrolyte may create a substantially thicker SEI layerof tens of microns than those found in conventional electrolytes of only1-100 nanometers. For example, FIG. 38 shows a porous layer ofapproximately 30 microns in thickness of lithium fluoride on the surfaceof lithium metal is created by soaking lithium metal in fluoromethanefor five. The porous nature of the layer shown by many cracks in thelayer could serve as high ionic conduction pathways down to the baselithium metal but also prevent dendrite formation, prolonging the lifeof a battery using a lithium metal anode.

Hence, some embodiments of this patent document include pretreating theelectrode materials in electrochemical energy storage devices with acompressed gas solvent to develop a beneficial SEI layer. This speciallygenerated SEI layer is useful in energy storage devices, particularlylithium-ion batteries, because this SEI layer provides an ionicallyconducting interface on the electrode such that ions can pass through itbut electrons cannot, thereby slowing or eliminating parasitic sidereactions including electrolyte breakdown by oxidation or reduction.Typically, the SEI layer is formed when an external voltage is appliedto the device, oxidizing and reducing the electrolyte on the respectiveelectrodes. At strongly reducing metals such as lithium metal, chemical(or electrochemical) reactions occur more easily, and hence little or noexternal voltage is required to develop the SEI layer because submersionof the metal into an electrolyte automatically carry out reductionwithout an externally applied voltage. Typically, SEI layers are formedwithin the already fully assembled device on first charge, and continueto gradually form with subsequent charge cycles. Some embodiments ofthis patent document use compressed gas solvent-based electrolytes todevelop this SEI formation in the already assembled device.

FIG. 41 presents a flowchart illustrating a process 4100 of preparing alithium metal electrode for an electrochemical energy storage device inaccordance with some embodiments.

The process 4100 includes submerging a lithium metal into a compressedgas solvent or a compressed gas electrolyte without applying an externalvoltage (4102). Next, while submerging, the process allows a SEI layerto form on the lithium metal surface as a result of the highly reducingproperties of lithium metal (4104). In some embodiments, the SEI layeron the lithium metal surface is oxygen-free. The lithium metal with theSEI layer is then removed from compressed gas solvent or a compressedgas electrolyte (4106), and subsequently assembled into anelectrochemical energy storage device as an lithium metal electrode(4108). While lithium metal is the preferred for its very high reducingproperties, other metals can be used in place of lithium metal, whichinclude magnesium, sodium and other metals with high reducingproperties.

FIG. 42 presents a flowchart illustrating a process 4200 of preparingelectrodes for an electrochemical energy storage device in accordancewith some embodiments. The process 4200

includes submerging a negative electrode or a positive electrode into acompressed gas electrolyte (4202). Next, an external voltage is appliedto the negative electrode or the positive electrode with anothersuitable counter electrode to form an SEI layer on the electrode (4204).The negative electrode or the positive electrode is then removed fromthe compressed gas electrolyte (4206) and subsequently assembled into anelectrochemical energy storage device as a negative electrode or apositive electrode (4208).

According to some embodiments of this patent disclosure, the benefit tousing a compressed gas solvent or electrolyte to build an SEI layer caninclude beneficiary SEI properties such as thinner or thicker SEI,improved ion conductivity, improved electrical resistance, improvedcycle life, oxygen free SEI, carbon free SEI, or other SEI free fromcertain unwanted elements or other such beneficial SEI properties.

Compressed Gas Electrolytes Based on Compressed Gas Solvent Mixtures

Another aspect of this patent document includes using co-solvents toform compressed gas electrolytes. Mixtures of two or more compressed gassolvents or mixtures of a single or multiple compressed gas solventswith a single or multiple liquid solvents is considered to also be acompressed gas solvent and can have beneficial properties for anelectrochemical device. For example, a single component compressed gassolvent may have higher solubility of a salt whereas a second singlecomponent compressed gas solvent may have improved temperatureperformance. Further, mixtures may lower or eliminate the flammabilityof the electrolyte system. The two may be mixed to give optimalproperties. Any number of compressed gas solvents may be mixed tooptimize device properties.

FIG. 43 shows conductivity vs. temperature data of a compressed gassolvent (without mixing) and two mixtures of various compressed gassolvents with 0.02 M TEABF₄ salt in accordance with some embodiments. Ascan be seen in FIG. 43, the three different compressed gas electrolytesare (1) difluoromethane, (2) difluoromethane and pentafluoroethane, and(3) difluoromethane and pentafluoromethane and tetrafluoromethane withthe latter two at different mixing levels. The two mixtures are shown tostill form ionically conducting electrolytes, though not as high as thesingle compressed gas solvent, may have other beneficial properties suchas SEI formation, wider potential window, better thermal properties orother beneficial properties.

For example, existing battery and supercapacitor technology often useshighly flammable electrolytes. These concerns have only been heightenedafter batteries in electric vehicles have ignited and caused vehicles tocatch fire, even with high safety standards. Various compressed gassolvents for electrolytes may be rendered non-flammable with mixtureswith other compressed gas solvents. For example, difluoromethane is aflammable solvent, however, mixtures of this with pentafluoroethane,tetrafluoroethane, or a number of other compressed gas solvents wouldcreate a non-flammable and safe mixture. The mixtures may be used aselectrolytes with non-flammable properties.

Protective Coating on Electrodes in Compressed Gas Electrolyte-BasedEnergy Storage Devices

The gradual degradation of Li-ion batteries (LIBs) operated at highpotential tends to limit the widespread and long-term applications ofsuch batteries. The interface between the solid electrode andelectrolyte interface (i.e., the SEI layer) needs to be improved toensure the desired long-term stability and safety. Stabilization of theelectrode surfaces can be accomplished by electrolyte additives andsurface coatings with a deposition of metal oxides or phosphates by achemical process or by conformal atomic layer deposition (ALD) coating.A thin, amorphous and conformal ALD coating of Al₂O₃ layer is typicallyachieved by using trimethylaluminum (TMA) precursor, with a typicalgrowth rate of 0.1 nm per cycle, which is well established. The ALDcoating can be applied onto either the surfaces of particles that makeup the electrodes or onto the final electrode surface.

In some embodiments of this disclosure, the electrodes (anode, cathodeor both) in compressed gas electrolyte-based batteries andsupercapacitors are improved by surface coatings for at least partialprotection from corrosion or undesirable side chemical reactions. Thiscan include a thin coating of carbon base material or preferably a thinatomic layer deposition (ALD) coating with aluminum oxide or other metaloxide or metal nitride. In some embodiments, the thickness of thecoating is at most 10 nm. In other embodiments, the thickness of thecoating is at most 3 nm. In yet other embodiments, the thickness of thecoating of at most 1 nm is preferred. Have such a coating can reduce theformation of undesirable soluble byproducts and to minimize the batterylife degradation.

Electroplating of Difficult-to-Electroplate Metals and Alloys

Another aspect of this patent document includes using compressed gaselectrolytes for electroplating metals. Electroplating is a metaldeposition process that uses electrical current to reduce dissolvedmetal cations so that they form a coherent metal coating on anelectrode. Electroplating is often used to enhance the surfaceproperties of an object (e.g., for corrosion resistance, wearresistance, improved appearance, and to add materials for variouspurposes.

In electroplating or electrodeposition, a power supply provides a directcurrent to the anode, oxidizing the metal atoms in the anode andallowing them to dissolve in the solution. At the cathode, the dissolvedmetal ions in the electrolyte solution are reduced at the interfacebetween the solution and the cathode, such that they “plate out” ontothe cathode. Some electroplating processes may use a non-consumableanode such as carbon or platinum.

Typically, metals (e.g., Cr, Ni, Cu, Au) are electroplated in aqueouselectrolytes because their plating potential is within, or close to, thepotential limits of water in acidic or basic conditions. Electroplatingof corrosion resistant or mechanically stronger metals such as Al, Tiand W, as well as semiconductor materials Si, Ge, etc. for facileelectronic device manufacturing. However, electrodeposition of thesesolvents in aqueous electrolytes is limited by the breakdown of water athigh potentials. For example, electrodeposition of germanium isdifficult because it requires a high cathodic potential, makingelectroplating from aqueous solutions almost impossible. Some metals,such as aluminum, are not capable of being plated in aqueous conditionsbecause they extend too far past this limit and or are quickly oxidizeddue to the aqueous environment. Other metals that have yet to havesignificant technical progress in electroplating are titanium, tungsten,silicon, gallium and germanium, along with others. The high reducingpotential needed for some metals, including titanium, make themincompatible in aqueous plating media and even many organic solventmedia. Some compressed gas solvents may show lower reduction potentialscapable of plating metallic titanium.

Example #4

FIG. 44 shows measurements of cyclic voltammetry curves of improvedpotential window for two electrolytes composed of 0.1 M1-Butyl-3-methylimidazolium Bis(trifluoromethylsulfonyl) Imide (BMITFSI)salt in compressed gas solvent difluoromethane and liquidous propylenecarbonate in accordance with some embodiments. As can be seen in FIG.44, the reduction potential of the propylene carbonate-based electrolyteoccurs at a much higher reduction potential of 1.5 V vs. Li, whereasdifluoromethane based electrolyte occurs at lower reduction potentialsof −0.5 V vs. Li. Because of the higher reduction potential of propylenecarbonate, titanium electroplating is incompatible in this media,whereas in the difluoromethane based electrolyte, electroplating may bemade possible.

Note that the high accessibility into nano sized pores of fluorinatedcompressed gas solvents can allow electrodeposition on nanoscalefeatures otherwise inaccessible to typical electroplating solutions. Insome embodiments of the patent disclosure, the nanopore accessibility ofthe compressed gas solvent-based energy storage or electroplatingdevices is improved by at least 10%, preferably by at least 30%, evenmore preferably by at least 100% as compared to the pore accessibilityof regular liquid solvent-based electrolytes. Furthermore, the highconductivity of such solutions can allow fast and efficientelectroplating of surfaces.

FIG. 45 illustrates an exemplary electroplating device structure fordepositing difficult-to-deposit metals or alloys, using compressed gassolvent-based electrolytes having lowered reduction potential inaccordance with some embodiments. As can be seen in FIG. 45, thehard-to-electroplate elements (Ti, Al, Si, W, Zr, Pt, etc.) can beelectroplated inside the compressed gas electrolyte that can dissolvethe metal-containing salt and that enables higher redox potential forthe electroplating electrochemical reaction. Note that theelectroplating device includes a pressure chamber wall includinginlet/output, valves, sensors to contain the compressed gaselectrolytes. Besides Ti, Si, Ge, Ga or their alloys, other relatedelements such as Zr, Hf, V, Nb, Ta or their alloys may also beconsidered capable of electroplating when using proper compressed gaselectrolytes and optimized plating conditions. Embodiments of thedisclosed techniques can reduce the reduction potential, by at least 5%,preferably 10% wider, even more preferably 20% than in the case ofelectroplating without using compressed gas solvent for the relevantmetallic salts.

For example, FIG. 46 shows a cyclic voltammogram of the electroplatingof titanium by reduction of TiCl₄ at a platinum metal surface in ancompressed gas electrolyte composed of electrolyte comprising of 0.1 MBMITFSI, 0.1 M TiCl₄ in difluoromethane in accordance with someembodiments. In this example, working and counter electrodes areplatinum metal, reference electrode is lithium metal with a 10 mV/ssweep rate. FIG. 46 shows many marked peaks in the cyclic voltammogramcorresponding to reduction of the TiCl₄ to the many oxidation states oftitanium with metallic titanium plating shown to occur at potentialslower than 1.2 V vs. Li. Further optimization of the plating can includefaster, more uniform or more pure titanium plating processes.

FIG. 47 presents a flowchart illustrating a process 4700 ofelectroplating difficult-to-deposit metals or alloys using compressedgas electrolytes as an electroplating bath in accordance with someembodiments. As shown in FIG. 47, to electroplate a difficult-to-depositmaterial on an object, a compressed gas electrolyte is first prepared bymixing a compressed gas solvent and one or more types of salts (4702),the compressed gas solvent used has the various properties as describedabove. Next, using the compressed gas electrolyte as anelectrodepositing bath, an anode made of at least thehard-to-electroplate material is immersed the compressed gas electrolyte(4704). A cathode made of an object that requires electroplating of thehard-to-electroplate material is also immersed in the compressed gaselectrolyte (4704). Next, a proper voltage is applied to the anode andthe cathode to allow transferring of the difficult-to-deposit materialfrom the anode to the cathode through the compressed gas electrolyte(4706). Moreover, the compressed gas electrolyte, the anode and thecathode are placed inside a pressure chamber which provides a requiredpressure to keep the compressed gas solvent in the liquid phase.

Improved EDLC Double Layer Supercapacitor Device Using Compressed GasSolvents

In some embodiments of this disclosure, an improved EDLC supercapacitordevice can be constructed using compressed gas electrolytes, and such anEDLC supercapacitor device can exhibit wider redox potential andassociated higher energy storage capability. FIG. 48 illustrates anexemplary higher-voltage supercapacitor device including electrochemicaldouble layer capacitors and using compressed gas electrolytes havingwider potential windows in accordance with some embodiments.

FIG. 49 shows three types of higher-voltage supercapacitor devices usingcompressed gas solvent-based electrolytes having wider potential windowsin accordance with some embodiments. As shown in FIG. 49, thesehigher-voltage supercapacitor devices include double-layersupercapacitors (i.e., electrostatic charge storage), pseudocapacitors(i.e., faradaic charge storage), and hybrid supercapacitors (i.e., bothelectrostatic and faradaic charge storage).

Improved Rechargeable Batteries Including Li-Ion Batteries UsingCompressed Gas Solvents

In some embodiments of this disclosure, an improved Li-ion battery canbe constructed, which exhibits wider redox potential and associatedhigher energy storage capability. FIG. 50 illustrates a schematic ofsuch a LiB energy storage device incorporated within pressure chamberstructure, with battery charging vs discharging reactions illustrated inaccordance with some embodiments. In the improved Li-ion batteries usingcompressed gas solvent-based electrolytes, the electrode performancescan be further improved in terms of longer life usage, with optionallysurface protection by artificial, preferably oxygen-free SEI layer, andalso are optionally comprise thin inorganic layer such as ALD depositedAl₂O₃ layer, which have been described above.

In some embodiments, batteries not based on lithium chemistry can alsobe constructed using compressed gas electrolytes. Such batteries may bebased on hydrogen, sodium or magnesium ion transfer (or their mixturesof ions) between electrodes or another similar battery chemistry thatcan store energy electrochemically. Consequently, disclosed embodimentsinclude similarly constructed devices, techniques of device fabricationand construction, mode of operation and applications of such non Li-ionbatteries.

In some embodiments, rechargeable batteries either based on lithiumchemistry or not based on lithium chemistry can be constructed usingcompressed gas electrolytes. In some embodiments, a disclosedrechargeable battery includes an anode selected from carbon-containingmaterials including: graphite, nanocarbon, carbon nanotubes, graphene,titanium-oxide-containing material such as nanostructured titaniumoxides or spinel lithium titanate, silicon and silicon alloys, tin andtin alloys, tin-cobalt alloys. In other embodiments, a disclosedrechargeable battery includes a composite anode that is made of one ormore carbon-containing materials including one or more of the followingmaterials: graphite, nanocarbon, carbon nanotubes, graphene,titanium-oxide-containing material such as nanostructured titaniumoxides or spinel lithium titanate, silicon and silicon alloys, tin andtin alloys, tin-cobalt alloys, and/or one or more conversion typematerials such as phosphides, nitrides, oxides, and sulfides.

In some embodiments, a disclosed rechargeable battery based on thecompressed gas electrolytes includes an anode which is made ofnanostructures selected from nanofibers, nanopillars, nanoparticleaggregates, nanoporous structures, or a combination of the above, andhaving a feature dimension of diameter or pore desirably less than 500nm, preferably less than 100 nm, even more preferably less than 60 nm.

In some embodiments, a surface of the anode of the disclosedrechargeable battery is protected from corrosion or undesirable sidechemical reactions by a thin coating of carbon base material orpreferably a thin atomic layer deposition (ALD) coating with aluminumoxide or other metal oxide or metal nitride, having a thickness of atmost 10 nm, preferably at most 3 nm, even more preferably at most 1 nm,so as to reduce the formation of undesirable soluble byproducts and tominimize the battery life degradation.

In some embodiments, the anode of the disclosed rechargeable battery hasa large surface area at least 500 m²/g, preferably at least 1,000 m²/g,even more preferably at least 2,000 m²/g, with an optional branch orhierarchical structure.

In some embodiments, the anode of the disclosed rechargeable batteryincludes nanopores, and the compressed gas electrolyte sufficientlypenetrates into the nanopores by means of a high pressure of thecompressed gas solvent to effectuate at least 10% enhanced energystorage capacity of the rechargeable battery, preferably at least 30%enhanced energy storage capacity as compared to an identicalnanostructured electrode based-on liquid-state electrolytes instead ofthe high pressure compressed gas solvent-based electrolytes.

In some embodiments, the disclosed rechargeable battery includes acathode made of a cathode material selected from lithium cobalt oxide,lithium nickel manganese cobalt oxide, spinnel type lithium manganeseoxide, lithium manganese nickel oxide, Olivine type lithium ironphosphate, lithium iron silicate, lithium iron fluoro sulfate, orselected from a group of conversion type cathode materials.

In some embodiments, the cathode is made of a cathode material selectedfrom conversion type metal fluorides of FeF₃, CrF₃, CrF₄, VF₃, VF₄,FeF₂, NiF₂, CoF₃, CuF₂, MnF₃, TiF₄, and BiF₃ in a bulk form, in ananostructured form or as nanocrystalline composites embedded in aconductive carbon matrix.

In some embodiments, the cathode is made of a cathode material selectedfrom silicates of Li₂MSiO₄ type formula where M is a transition metalsuch as Fe, Ni, Co, Mn, or selected from sulfates of LiMSO₄O (M=Fe, Ni,Co, Mn), or selected from phosphates of LiMPO₄O (M=Fe, Ni, Co, Mn).

In some embodiments, a disclosed rechargeable battery has an operatingbattery redox potential window which is at least 4.5V, preferably atleast 4.8 volt, even more preferably at least 5.2V.

In some embodiments, a surface of the cathode of the disclosedrechargeable battery is protected from corrosion or undesirable sidechemical reactions by a thin coating of carbon base material orpreferably a thin ALD coating with aluminum oxide or other metal oxideor metal nitride, having a thickness of at most 10 nm, preferably atmost 3 nm, even more preferably at most 1 nm, so as to reduce theformation of undesirable soluble byproducts and to minimize the batterylife degradation.

In some embodiments, the cathode of the disclosed rechargeable batteryhas a large surface area at least 500 m²/g, preferably at least 1,000m²/g, even more preferably at least 2,000 m²/g, with an optional branchor hierarchical structure.

In some embodiments, the disclosed the rechargeable battery exhibitshigher capacity by at least 50%, preferably by a factor of at least two,as compared to graphite-anode type Li-ion battery which is effectuatedby: (1) incorporating an anode made of metallic Li, or an alloy of Limetal containing at least atomic 50% Li, or a composite anode containingat least atomic 50% Li; and (2) having the anode metal electrode surfaceprotected by a thin layer coating of Al₂O₃ at most 10 nm, preferably atmost 3 nm, even more preferentially at most 1 nm, so as to minimizeundesirable chemical reaction or corrosion reaction.

In some embodiments, the rechargeable battery exhibits higher capacityby at least 50%, preferably by a factor of at least two, as compared tographite-anode type Li-ion battery, which is effectuated by the anodewhich is coated with a protective material having a thickness of at most20 nm, preferably at most 6 nm, even more preferentially at most 2 nm,that allows passage of Li-ions. This anode is an ionic conductor innature, with the coating material comprising polymeric component orcomplex oxide component. In some embodiments, the protective material isa solid-electrolyte-interface (SEI) layer which contains no oxygen forenhanced long term reliability.

Global Warming Potential Aspect

Some of the hydrofluorocarbon and related compounds are known tofunction like a greenhouse gas and contribute to the global warming, andhence there is an effort to reduce or eliminate use of suchhydrofluorocarbon compounds. Global-warming potential (GWP) is arelative measure of how much heat a greenhouse gas traps in theatmosphere. It compares the amount of heat trapped by a certain mass ofthe gas_in question to the amount of heat trapped by a similar mass ofcarbon dioxide. GWP is expressed as a factor of carbon dioxide (whoseGWP is standardized to 1).

In an aspect of this patent disclosure, compressed gas solvents having arelatively low GWP value is desirable (see the table entry in FIG. 12).For example, the hydrofluorocarbon molecule of the compressed gassolvent having preferably two or less fluorine atoms, preferably havingone fluorine atom is desirable, such as in the case of fluoromethane,fluoroethane, fluoropropane rather than difluoromethane ordifluoroethane or difluoropropane (though use of two-fluorine atomcompressed gas solvents is not excluded). For example, Li salt has beenshown to conduct well in at least two compressed gas solvents having lowGWP, such as fluoromethane (GWP=90) and fluoroethane (GWP is only 12).Fluoropropane solvent (GWP possibly<12) may be another possibility.

High Pressure Aspects in Compressed Gas Solvent Devices

The various compressed gas solvents used in the disclosed compressed gassolvent-based electrolyte devices including supercapacitors, batteries,electroplating systems are inherently non-toxic, safe, and commerciallyavailable (therefore relatively inexpensive), and can be madenon-flammable, when mixed in well-known azeotropic mixtures offluorinated compressed gas solvents. Being a compressed gas solvent,high pressure containment is an aspect that needs some attention.However, even the most volatile of the compounds in this class ofhydrofluorocarbon type solvents has a room temperature vapor pressure of˜400 psi (˜27.2 atmosphere), a moderate pressure at best. It isnoteworthy that there are automobiles that run on regular compressedair, for example, Tata's cars in India that operate with pressures of upto ˜5,000 psi (˜340 atmosphere), which is safely contained in cylinders.In order to provide some safety margin, the compressed gas solvent-basedelectrolyte devices can be limited to operate at a pressure less than1,000 atmospheres, preferably less than 200 atmospheres, even morepreferably less than 50 atmospheres.

In some aspects of the disclosed technology, disclosed are newelectrolytes, and methods for fabricating and implementing devices usingsuch electrolytes, based on compressed gas solvents. Such devices mayhave wide electrochemical potentials, high conductivity, low temperaturecapability or beneficial high pressure solvent properties. Someexemplary applications include electrochemical energy storage devicessuch as batteries or supercapacitors, electroplating and electrochemicalsensing.

While this patent document contains many specifics, these should not beconstrued as limitations on the scope of any invention or of what may beclaimed, but rather as descriptions of features that may be specific toparticular embodiments of particular inventions. Certain features thatare described in this patent document in the context of separateembodiments can also be implemented in combination in a singleembodiment. Conversely, various features that are described in thecontext of a single embodiment can also be implemented in multipleembodiments separately or in any suitable subcombination. Moreover,although features may be described above as acting in certaincombinations and even initially claimed as such, one or more featuresfrom a claimed combination can in some cases be excised from thecombination, and the claimed combination may be directed to asubcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings in a particularorder, this should not be understood as requiring that such operationsbe performed in the particular order shown or in sequential order, orthat all illustrated operations be performed, to achieve desirableresults. Moreover, the separation of various system components in theembodiments described in this patent document should not be understoodas requiring such separation in all embodiments.

Only a few implementations and examples are described and otherimplementations, enhancements and variations can be made based on whatis described and illustrated in this patent document.

What is claimed are techniques and structures as described and shown,including:
 1. An electrochemical device, comprising: an ionicallyconducting electrolyte comprising a compressed gas solvent and one ormore types of salts, wherein the compressed gas solvent includes amaterial that is in a gas phase and has a vapor pressure above anatmospheric pressure at a room temperature; a housing enclosing theionically conducting electrolyte and structured to provide a pressurizedcondition to the compressed gas solvent; and a pair of conductingelectrodes in contact with the ionically conducting electrolyte.
 2. Theelectrochemical device of claim 1, wherein the ionically conductingelectrolyte includes a mixture of two or more types of solventsincluding the compressed gas solvent and at least one liquid solvent. 3.The electrochemical device of claim 1, wherein the ionically conductingelectrolyte includes a mixture of two or more types of solventsincluding at least two types of compressed gas solvents.
 4. Theelectrochemical device of claim 1, wherein each of the one or more typesof salts is in either solid or liquid form before mixing with thecompressed gas solvent.
 5. The electrochemical device of claim 1,wherein the compressed gas solvent has a boiling point temperature lessthan room temperature of 293.15 K.
 6. The electrochemical device ofclaim 1, wherein the compressed gas solvent is in a liquid phase in theionically conducting electrolyte, and wherein the compressed gas solventis under a compressive pressure equal to or greater than a vaporpressure of the compressed gas solvent at an operating temperature. 7.The electrochemical device of claim 1, wherein the compressed gassolvent includes one of more of the following chemicals:hydrofluorocarbon, fluorine partially of wholly substituted withchlorine, iodine, bromide, ammonia, nitrous oxide, molecular oxygen,molecular nitrogen, carbon dioxide, carbon monoxide, hydrogen fluoride,and hydrogen chloride.
 8. The electrochemical device of claim 1, whereinthe electrochemical device is an energy storage device, wherein the pairof conducting electrodes includes: a negative electrode comprising: anegative current collector; and negative electrode material coated onthe negative current collector; a positive electrode comprising: apositive current collector; and positive electrode material coated onthe positive current collector; and wherein the energy storage devicefurther includes an electrically insulating placed separator between thepair of conducting electrodes.
 9. The electrochemical device of claim 8,wherein one or both of the negative electrode material and the positiveelectrode material include nanostructured material to form high surfacearea electrode, which includes one or more of: nanofibers; nanopillars;nanoparticle aggregates; nanoporous structures; and a combination of theabove.
 10. The electrochemical device of claim 8, wherein the energystorage device is a supercapacitor having a potential window of at least3.0 V, and an operating temperature range of from minus 80° C. to plus60° C.
 11. The electrochemical device of claim 10, wherein the capacitoris an electrochemical supercapacitor which stores energy based on oneof: electrostatic charge storage using a structure of electrochemicaldouble layer capacitor (EDLC); Faradaic charge storage; and a hybridstorage of electrostatic charge storage and Faradaic charge storage. 12.The electrochemical device of claim 8, wherein one or both of thenegative electrode material and the positive electrode material comprisenanopores, and charged ions in the electrolyte penetrate into thenanopores by mean of being subject to a high pressure in the compressedgas solvent, wherein the high pressure is greater than the atmosphericpressure of 100 kPa, preferably 10×the atmospheric pressure, or morepreferably 20×the atmospheric pressure, resulting in an enhanced energystorage capacity.
 13. The electrochemical device of claim 12, whereinthe compressed gas solvent is selected to have a high vapor pressure tofacilitate higher ion access to the nanopores by at least 10% more,preferably 30% more, and even more preferably 50% more.
 14. Theelectrochemical device of claim 8, wherein the energy storage device isa rechargeable battery comprising an anode and a cathode.
 15. Theelectrochemical device of claim 14, wherein the anode is made of ananode material selected from carbon-containing materials including:graphite, nanocarbon, carbon nanotubes, graphene,titanium-oxide-containing material such as nanostructured titaniumoxides or spinel lithium titanate, silicon and silicon alloys, tin andtin alloys, tin-cobalt alloys.
 16. The electrochemical device of claim14, wherein the anode is a composite anode which is made of one or morecarbon-containing materials including one or more of the followingmaterials: graphite, nanocarbon, carbon nanotubes, graphene,titanium-oxide-containing material such as nanostructured titaniumoxides or spinel lithium titanate, silicon and silicon alloys, tin andtin alloys, tin-cobalt alloys, and/or one or more conversion typematerials such as phosphides, nitrides, oxides, and sulfides.
 17. Theelectrochemical device of claim 14, wherein the anode is made ofnanostructures selected from nanofibers, nanopillars, nanoparticleaggregates, nanoporous structures, or a combination of the above, andhaving a feature dimension of diameter or pore desirably less than 500nm, preferably less than 100 nm, even more preferably less than 60 nm.18. The electrochemical device of claim 14, wherein a surface of theanode is protected from corrosion or undesirable side chemical reactionsby a thin coating of carbon base material or preferably a thin atomiclayer deposition (ALD) coating with aluminum oxide or other metal oxideor metal nitride, having a thickness of at most 10 nm, preferably atmost 3 nm, even more preferably at most 1 nm, so as to reduce theformation of undesirable soluble byproducts and to minimize the batterylife degradation.
 19. The electrochemical device of claim 14, whereinthe anode has a large surface area at least 500 m²/g, preferably atleast 1,000 m²/g, even more preferably at least 2,000 m²/g, with anoptional branch or hierarchical structure.
 20. The electrochemicaldevice of claim 14, wherein the anode includes nanopores, wherein theelectrolyte sufficiently penetrates into the nanopores by means of ahigh pressure of the compressed gas solvent to effectuate at least 10%enhanced energy storage capacity of the rechargeable battery, preferablyat least 30% enhanced energy storage capacity as compared to anidentical nanostructured electrode based-on liquid-state electrolytesinstead of the high pressure compressed gas solvent-based electrolytes.21. The electrochemical device of claim 14, wherein the cathode is madeof a cathode material selected from lithium cobalt oxide, lithium nickelmanganese cobalt oxide, spinnel type lithium manganese oxide, lithiummanganese nickel oxide, Olivine type lithium iron phosphate, lithiumiron silicate, lithium iron fluoro sulfate, or selected from a group ofconversion type cathode materials.
 22. The electrochemical device ofclaim 14, wherein the cathode is made of a cathode material selectedfrom conversion type metal fluorides of FeF₃, CrF₃, CrF₄, VF₃, VF₄,FeF₂, NiF₂, CoF₃, CuF₂, MnF₃, TiF₄, and BiF₃ in a bulk form, in ananostructured form or as nanocrystalline composites embedded in aconductive carbon matrix.
 23. The electrochemical device of claim 14,wherein the cathode is made of a cathode material selected fromsilicates of Li₂MSiO₄ type formula where M is a transition metal such asFe, Ni, Co, Mn, or selected from sulfates of LiMSO₄O (M=Fe, Ni, Co, Mn),or selected from phosphates of LiMPO₄O (M=Fe, Ni, Co, Mn).
 24. Theelectrochemical device of claim 14, wherein the rechargeable battery hasan operating battery redox potential window which is at least 4.5V,preferably at least 4.8 volt, even more preferably at least 5.2V. 25.The electrochemical device of claim 14, wherein the surface of thecathode is protected from corrosion or undesirable side chemicalreactions by a thin coating of carbon base material or preferably a thinALD coating with aluminum oxide or other metal oxide or metal nitride,having a thickness of at most 10 nm, preferably at most 3 nm, even morepreferably at most 1 nm, so as to reduce the formation of undesirablesoluble byproducts and to minimize the battery life degradation.
 26. Theelectrochemical device of claim 14, wherein the cathode has a largesurface area at least 500 m²/g, preferably at least 1,000 m²/g, evenmore preferably at least 2,000 m²/g, with an optional branch orhierarchical structure.
 27. The electrochemical device of claim 14,wherein the rechargeable battery exhibits higher capacity by at least50%, preferably by a factor of at least two, as compared tographite-anode type Li-ion battery, which is effectuated by:incorporating an anode made of metallic Li, or an alloy of Li metalcontaining at least atomic 50% Li, or a composite anode containing atleast atomic 50% Li; with optionally having the anode metal electrodesurface protected by a thin layer coating of Al₂O₃ at most 10 nm,preferably at most 3 nm, even more preferentially at most 1 nm, so as tominimize undesirable chemical reaction or corrosion reaction.
 28. Theelectrochemical device of claim 14, wherein the rechargeable batteryexhibits higher capacity by at least 50%, preferably by a factor of atleast two, as compared to graphite-anode type Li-ion battery, which iseffectuated by the anode which is coated with a protective materialhaving a thickness of at most 100 nm, desirably at most 20 nm,preferably at most 6 nm, even more preferentially at most 2 nm, thatallows passage of Li-ions, and wherein the anode is an ionic conductorin nature, with the coating material comprising polymeric component orcomplex oxide component.
 29. The electrochemical device of claim 28,wherein the protective material is a solid-electrolyte-interface (SEI)layer which contains no oxygen for enhanced long term reliability. 30.The electrochemical device of claim 14, wherein the rechargeable batteryincludes a lithium (Li)-ion battery having an operating temperaturerange from minus 80° C. to plus 60° C.
 31. The electrochemical device ofclaim 1, wherein the housing is a rigid housing.
 32. The electrochemicaldevice of claim 31, further comprising one or more ports pass-throughthe rigid housing for inserting compressed gas solvent into the device.33. The electrochemical device of claim 1, further comprising a pressurecontroller for controlling an applied pressure on the ionicallyconducting electrolyte.
 34. The electrochemical device of claim 1,further comprising one or more electrical sensors for monitoringenvironmental conditions of the electrochemical device.
 35. Theelectrochemical device of claim 1, wherein the compressed gas solvent isselected to have a melting point significantly lower than a meltingpoint of a common solvent.
 36. The electrochemical device of claim 1,wherein the compressed gas solvent is placed under a compressivepressure equal to, or greater than the compressed gas's vapor pressureat a temperature when the compressive pressure is applied, therebykeeping the compressed gas solvent in a liquid phase.
 37. Theelectrochemical device of claim 36, wherein the compressive pressure iseffectuated by the vapor pressure of the compressed gas solvent or by anexternally applied pressure.
 38. The electrochemical device of claim 1,wherein the electrochemical device is contained inside a high pressurechamber with an operating pressure of less than 1,000 atmospheres,preferably less than 200 atmospheres, even more preferably less than 50atmospheres.
 39. A method for constructing an electrochemical cell,comprising: mixing a compressed gas solvent and one or more types ofsalts into a pressurized container to form a compressed gas electrolyte;and placing electrodes in contact with the compressed gas electrolyte toform an electrochemical cell.
 40. The method of claim 39, wherein thecompressed gas solvent has a vapor pressure above atmospheric pressureof 100 kPa at room temperature of 293.15 K.
 41. The method of claim 39,wherein electrochemical electrode assembly comprises: a negative currentcollector; negative electrode material coated on the negative currentcollector; a positive current collector; positive electrode materialcoated on the positive current collector; and an electrically insulatingseparator between the negative electrode material and the positiveelectrode material.
 42. A method for constructing an electrochemicalcell, comprising: inserting one or more types of salts into anelectrochemical electrode assembly to form a salt loaded electrochemicalelectrode assembly; and introducing a compressed gas solvent into thesalt loaded electrochemical electrode assembly inside a high pressurehousing to be mixed with the one or more types of salts to create acompressed gas electrolyte inside the high pressure housing, therebyforming an operating electrochemical cell.
 43. A method for preparing ametal electrode for an electrochemical energy storage device,comprising: submerging a metal into a compressed gas solvent or acompressed gas electrolyte; while submerging, allowing a solidelectrolyte interfaces (SEI) layer to form on a surface of the metal asa result of a highly reducing property of the metal; and removing themetal coated with the SEI layer from the compressed gas solvent or thecompressed gas electrolyte.
 44. The method of claim 43, furthercomprising assembling the metal into an electrochemical energy storagedevice as metal electrode.
 45. The method of claim 43, wherein the metalis an active metal including lithium, sodium, magnesium, and otheractive metals.
 46. The method of claim 45, wherein the electrochemicalenergy storage device is a lithium-ion battery.
 47. The method of claim42, wherein while submerging, the method further comprise applying anexternal voltage on the metal.
 48. The method of claim 43, wherein thecompressed gas solvent has a vapor pressure above atmospheric pressureof 100 kPa at room temperature of 293.15 K.
 49. The method of claim 43,wherein the compressed gas electrolyte is formed by mixing a compressedgas solvent and one or more types of salts.
 50. A method forelectrodepositing difficult-to-deposit metals or alloys, comprising:preparing an electrodepositing bath by forming a compressed gaselectrolyte by mixing a compressed gas solvent and one or more types ofsalts; immersing an anode made of at least a hard-to-electroplatematerial in the compressed gas electrolyte; immersing a cathode made ofan object that requires electroplating of the hard-to-electroplatematerial in the compressed gas electrolyte; and applying a voltage tothe anode and the cathode to allow transferring of thedifficult-to-deposit material from the anode to the cathode through thecompressed gas electrolyte.
 51. The method of claim 50, wherein thecompressed gas electrolyte, the anode and the cathode are placed insidea pressure chamber for providing an external pressure on the compressedgas solvent.
 52. The method of claim 50, wherein thehard-to-electroplate material includes Ti, Zr, Nb, Mo, Hf, Ta, W, Re,Os, Al, Mg, Ca, Si, Ge and the alloys of the above.
 53. Anelectrochemical device, comprising: electrodes; and an electrolyte incontact with the electrodes and comprising a compressed gas solvent. 54.The electrochemical device of claim 53, wherein an operating potentialwindow of the electrochemical device is improved by at least 5%,preferably by at least 20% as compared to electrochemical devicescontaining non-compressed-gas based solvent.
 55. The electrochemicaldevice of claim 53, wherein the electrochemical device includessupercapacitors, such as electrochemical double-layer capacitors (EDLC).56. The electrochemical device of claim 53, wherein the electrochemicaldevice includes batteries, such as Li-ion batteries and other types ofbatteries.
 57. The electrochemical device of claim 53, wherein theoperating temperature range is increased with the cold temperature rangeextended to at least −50° C., preferably to at least −70° C.
 58. Theelectrochemical device of claim 53, wherein the compressed gas solventsolvent of the electrochemical device is selected from hydrofluorocarbonor hydrofluoroolefin based material with Global Warming potential (GWP)of less than 1,000, preferably less than 200, even more preferably lessthan
 20. 59. The electrochemical device of claim 53, wherein if selectedfrom the hydrofluorocarbon-based material, the hydrofluorocarbonmolecule has preferably one fluorine atom, such as in the case offluoromethane, fluoroethane, fluoropropane and, as compared todifluoromethane or difluoroethane or difluoropropane.
 60. An electrolytefor use in an electrochemical, electrodeposition, or electrochemicalsensing device, comprising: a compressed gas solvent; and one or morenon-metal-ion-containing salts if used for supercapacitors devices; orone or more metal-ion-containing salts if used for battery devices andelectrodeposition devices.
 61. The electrolyte of claim 60, wherein thecompressed gas solvent is selected from hydrofluorocarbon, or fluorinepartially of wholly substituted with chlorine, iodine, bromide, or fromammonia or nitrous oxide, molecular oxygen, molecular nitrogen, carbondioxide, carbon monoxide, hydrogen fluoride or hydrogen chloride. 62.The electrolyte of claim 60, wherein the non-metal-containing salt areselected from carbonates, fluoroborates, perchlorates, phosphates suchas TEA, TBA, ClO₄, BF₄ or PF₆ for supercapacitor devices.
 63. Theelectrolyte of claim 60, wherein the metal-ion-containing salts areselected from salts containing Li, Na, Si, Ga, Ge, Al, Ti, W, Zr, Hf, V,Nb, Ta or their combinations for battery devices or electrodeposition.64. A lithium (Li)-ion battery, comprising: a pair of electrodes; and anelectrolyte in contact with the pair of electrodes; wherein at least oneelectrode of the pair of electrodes includes a solid electrolyteinterfaces (SEI) layer formed on a surface of the at least one electrodeas a result of a highly reducing property of the electrode material. 65.The Li-ion battery claim 64, wherein the SEI layer is substantially freeof oxygen.
 66. The Li-ion battery claim 65, wherein the SEI layer hasone or both of a lithium fluoride (LiF) layer and a polymer layer. 67.The Li-ion battery claim 64, wherein the at least one electrode reducesLi metal dendrite formation by at last 10%, preferably 30%, even morepreferably at least 50% as compared to an Li metal electrode without anSEI layer.
 68. The Li-ion battery claim 64, wherein the electrolytecomprises a compressed gas solvent and one or more types of salts, andwherein the SEI layer is formed while immersed in the compressed gassolvent-based electrolyte.
 69. The Li-ion battery claim 68, wherein theelectrolyte comprises a liquid solvent and one or more types of salts,and wherein the SEI layer is formed while immersed in the liquidsolvent-based electrolyte.
 70. The Li-ion battery claim 69, wherein theSEI layer formed while immersed in a liquid solvent-based electrolytereduces Li metal dendrite formation by at last 10%, preferably 30%, morepreferably at least 50%, and even more preferably at least 80% ascompared to the SEI layer formed while immersed in the liquidsolvent-based electrolyte.
 71. A lithium (Li)-ion battery, comprising:an anode; a cathode; and a liquid solvent-based electrolyte in contactwith the anode and cathode; wherein the anode is pretreated to include asolid electrolyte interfaces (SEI) layer on a surface of the anode as aresult of immersing a Li metal within a compressed gas solvent-basedelectrolyte prior to inserting the anode into the Li-ion battery.